Time trends in the incidence of renal carcinoma: analysis of Connecticut Tumor Registry data, 1935-1989

Recent trends in the incidence of renal cancer, stratified by histology, have not been reported. This study utilized data from the Connecticut Tumor Registry (CTR), the oldest population-based cancer registry in the United States, to establish time trends in the incidence of adenocarcinoma and transitional cell carcinoma of the kidney and urinary tract. All 10,209 incident cases of renal cancer reported to the CTR between 1935 and 1989 were analyzed. Regression modelling was employed to determine the effects of age, period, and birth cohort on incidence rates, and to project future trends. The incidence rate of adenocarcinoma increased in females from 0.7/100,000 in 1935-39, to 4.2/100,000 in 1985-89; and in males, from 1.6/100,000 in 1935-39, to 9.6/100,000 in 1985-89. The reported incidence of transitional cell carcinoma increased in males from 0.5/100,000 in 1950-54 to 2.8/100,000 in 1985-89, and in females from 0.2/100,000 to 1.1/100,000 over the same period. Regression modelling revealed that both net and recent drift, the sum of period and cohort slopes, were positive for adenocarcinoma in both sexes, largely due to a positive cohort effect. While the net drift for transitional cell carcinoma was positive, recent drift was negative in both sexes due primarily to a negative cohort effect. Incidence rates of adenocarcinoma are likely to rise in the immediate future, with the rate of rise in females possibly exceeding that in males. Incidence rates of transitional cell carcinoma will stabilize.

Malignant melanoma incidence in Connecticut (United States): time trends and age-period-cohort modeling by anatomic site

This study examined time trends and age-period-cohort patterns in the incidence of cutaneous malignant melanoma (CMM) by gender and anatomic site in Connecticut (United States) between 1950 and 1989, using data from the population-based Connecticut Tumor Registry. A total of 8,249 invasive CMM incident cases were included. Cases were grouped into melanomas of the head and neck, upper limb, lower limb, and trunk. Between 1950 and 1989, rates increased substantially for all sites. The largest relative increases occurred in melanoma of the upper limb for both males and females; the largest absolute increase occurred for melanoma of the trunk in males; and the smallest increase occurred in head and neck melanoma in females. Recent trends for time periods 1970-89 among birth cohorts 1930-69 indicated that the rate of increase of CMM is slowing substantially among males, but not among females. Nevertheless, continued overall increases in CMM incidence are likely in Connecticut in the 1990s in both genders, with a decrease in the male-female ratio. The age-period-cohort patterns were significantly different between the genders and among anatomic sites, suggesting different trends in carcinogenic exposures (mainly ultraviolet radiation from the sun) or etiologic distinctions between males and females and among the sites.

Estimating age, period and cohort effects using the multistage model for cancer

To understand cancer aetiology better, epidemiologists often try to investigate the time trends in disease incidence with year of diagnosis (period) and birth cohort. Unfortunately, one cannot identify these factors uniquely in the usual regression model owing to a linear dependence between age, period and cohort, so that one requires additional information about the underlying biology of the disease. Carcinogenesis models provide one type of information that can result in a unique set of parameters for the effects of age, period and cohort. We use the multistage carcinogenesis model and its extensions to obtain a unique set of parameters for an age-period-cohort model of lung cancer trends of Connecticut males and females from 1935 to 1988. Some of these models do not seem to provide a reasonable set of model parameters, but we found that a model that included second-order terms and a multistage mixture model both gave a good fit to the data and realistic parameter estimates.

Effects of timing of methylprednisolone or naloxone administration on recovery of segmental and long-tract neurological function in NASCIS 2

Previous analyses of the National Acute Spinal Cord Injury Study (NASCIS) have not distinguished recovery of segmental function at the injury level from recovery of the long spinal tracts. Recovery at the injury level could be of considerable clinical significance, but long-tract recovery is the ultimate therapeutic goal. This analysis demonstrates that the greatest proportion of all neurological recovery and of recovery due to treatment with very high doses of methylprednisolone within 8 hours of injury occurs below the lesion. Methylprednisolone treatment administered early following injury has been found to improve recovery below the lesion in patients initially diagnosed as having complete or incomplete injuries; it also leads to greater (but still relatively small) improvement in the injury level. The analysis indicates that delayed treatment with methylprednisolone is associated with decreased neurological recovery. Naloxone administration also improved neurological function below the lesion in patients with incomplete injuries; these results support further experimental work with this drug. This observation of differential neurological response within a narrow treatment window has important implications for both experimental studies and clinical management. Early clinical management with high-dose methylprednisolone is supported by this analysis.

The time trend and age-period-cohort effects on incidence of adenocarcinoma of the stomach in Connecticut from 1955-1989

BACKGROUND

Adenocarcinoma of the gastric cardia has been be increasing in Connecticut, and the risk factors responsible for the increasing incidence are unknown. This study examined the incidence pattern of adenocarcinoma of the gastric cardia and distal stomach in Connecticut during the past decades and identified components of birth cohort, period, and age as determinants of the observed time trends by regression modeling.

METHODS

This study was based on all histologically confirmed incident cases of gastric adenocarcinoma reported to the Connecticut Tumor Registry between 1955 and 1989. Stomach cancers were grouped into cancers of the gastric cardia, distal stomach, or unknown/unspecified subsite. Age-adjusted incidence rates were calculated by the direct method standardized to the 1970 United States population. A regression model was used to identify birth cohort, period, and age as determinants of the observed time trends.

RESULTS

The results indicated that the incidence rate of adenocarcinoma of the cardia is increasing, particularly in white males, whereas adenocarcinoma of the distal stomach is now decreasing in both sexes in Connecticut. Regression modeling suggests that the increase of adenocarcinoma of the cardia may be explained partly by a birth cohort phenomenon.

CONCLUSION

There is little information regarding the risk factors that might be responsible for the observed increasing trend for adenocarcinoma of the cardia, although smoking, alcohol intake, retinol intake, and hiatal hernia have been associated with an increased risk of adenocarcinoma of the cardia or gastric cancer. Considering the different epidemiologic features of adenocarcinoma of the cardia and distal stomach, future analytic studies should separate cancer of the gastric cardia and cancer of the distal stomach in searching for etiologic factors.

The time trend and age-period-cohort effects on incidence of adenocarcinoma of the stomach in Connecticut from 1955-1989

BACKGROUND

Adenocarcinoma of the gastric cardia has been be increasing in Connecticut, and the risk factors responsible for the increasing incidence are unknown. This study examined the incidence pattern of adenocarcinoma of the gastric cardia and distal stomach in Connecticut during the past decades and identified components of birth cohort, period, and age as determinants of the observed time trends by regression modeling.

METHODS

This study was based on all histologically confirmed incident cases of gastric adenocarcinoma reported to the Connecticut Tumor Registry between 1955 and 1989. Stomach cancers were grouped into cancers of the gastric cardia, distal stomach, or unknown/unspecified subsite. Age-adjusted incidence rates were calculated by the direct method standardized to the 1970 United States population. A regression model was used to identify birth cohort, period, and age as determinants of the observed time trends.

RESULTS

The results indicated that the incidence rate of adenocarcinoma of the cardia is increasing, particularly in white males, whereas adenocarcinoma of the distal stomach is now decreasing in both sexes in Connecticut. Regression modeling suggests that the increase of adenocarcinoma of the cardia may be explained partly by a birth cohort phenomenon.

CONCLUSION

There is little information regarding the risk factors that might be responsible for the observed increasing trend for adenocarcinoma of the cardia, although smoking, alcohol intake, retinol intake, and hiatal hernia have been associated with an increased risk of adenocarcinoma of the cardia or gastric cancer. Considering the different epidemiologic features of adenocarcinoma of the cardia and distal stomach, future analytic studies should separate cancer of the gastric cardia and cancer of the distal stomach in searching for etiologic factors.

Age-period-cohort modelling of large-bowel-cancer incidence by anatomic sub-site and sex in Connecticut

In order to investigate etiologic distinctions among the anatomic sub-sites of the large bowel by sex, the relationship between large-bowel-cancer incidence and age at diagnosis, time period at diagnosis, and birth cohort was analyzed by anatomic sub-site and by sex, using data from the Connecticut Tumor Registry. Included in the study were all incident large-bowel-cancer cases occurring between 1950 and 1984 among Connecticut residents aged 40 to 79. Cancers of the large bowel were classified into 5 anatomic sub-sites: ascending colon (including cecum), transverse colon (including flexures), descending colon, sigmoid colon, and rectum (including rectosigmoid junction, anal canal, and anus). The data were fitted to log-linear age-period-cohort models. For each of the sub-sites, the age-period-cohort patterns for males and females differed. Within each sex, sub-site groupings with common patterns were indicated. Among males, the age-period-cohort patterns for the colon sub-sites were fairly similar; but the pattern for the rectum differed markedly from that for the colon sub-sites. There were secondary differences among the colon sub-sites that pointed to a secondary distinction between the right and the left colons. Among females, the age-period-cohort patterns for the left colon sub-sites and the rectum were fairly similar. The pattern for the transverse colon differed moderately from that of the left colon, and differed substantially from that of the rectum and the ascending colon. The ascending colon differed markedly from each of the other sub-sites. It is possible that these differences in age-period-cohort patterns reflect etiologic distinctions among sub-site groupings and between the sexes.

The risk of determining risk with multivariable models

PURPOSE

To review the principles of multivariable analysis and to examine the application of multivariable statistical methods in general medical literature.

DATA SOURCES

A computer-assisted search of articles in The Lancet and The New England Journal of Medicine identified 451 publications containing multivariable methods from 1985 through 1989. A random sample of 60 articles that used the two most common methods--logistic regression or proportional hazards analysis--was selected for more intensive review.

DATA EXTRACTION

During review of the 60 randomly selected articles, the focus was on generally accepted methodologic guidelines that can prevent problems affecting the accuracy and interpretation of multivariable analytic results.

RESULTS

From 1985 to 1989, the relative frequency of multivariable statistical methods increased annually from about 10% to 18% among all articles in the two journals. In 44 (73%) of 60 articles using logistic or proportional hazards regression, risk estimates were quantified for individual variables ("risk factors"). Violations and omissions of methodologic guidelines in these 44 articles included overfitting of data; no test of conformity of variables to a linear gradient; no mention of pertinent checks for proportional hazards; no report of testing for interactions between independent variables; and unspecified coding or selection of independent variables. These problems would make the reported results potentially inaccurate, misleading, or difficult to interpret.

CONCLUSIONS

The findings suggest a need for improvement in the reporting and perhaps conducting of multivariable analyses in medical research.

Analysing the temporal effects of age, period and cohort

Longitudinal trends can be analysed in terms of the effect of age, birth cohort or year of diagnosis. All three temporal effects are thought to be useful by epidemiologists, but they are not identifiable when assessed simultaneously. Partitioning the effects in terms of linear and curvature components is one approach to understanding the problem and finding a reasonable summary of trends. Other solutions can be expressed in terms of these components, and they can also be used to understand both subgroup and temporal interactions. One approach that may offer a way of understanding the effect of risk factor trends on population based rates is to use models that incorporate an effect due to the risk factors. These methods are discussed using lung cancer incidence and mortality to illustrate the underlying concepts.

The genetic epidemiology of second primary breast cancer

It is well established that women with a family history of breast cancer run a higher risk of breast cancer than do women without a family history. The evidence, however, is less clear regarding a possible association between a family history of breast cancer and risk of second primaries. The purpose of this prospective study was to estimate the risk for second primary breast cancer associated with having a family history of breast, endometrial, and ovarian cancers. A cohort of 4,660 women with a first primary breast cancer diagnosed between 1980 and 1982 were interviewed as part of the Cancer and Steroid Hormone Study, a multi-center population-based case-control study, and followed through eight Surveillance, Epidemiology, and End Results (SEER) program registries for 4 to 6 years. Of these women, 136 developed a second primary breast cancer in the contralateral breast at least 6 months after diagnosis of the first primary. Cox proportional hazards modeling techniques were used to model the time to onset of second primary breast cancer while adjusting for multiple predictors. The risk of contralateral breast cancer was elevated among cohort members who reported a history of breast cancer in a first-degree relative (multivariable-adjusted rate ratio (RR) = 1.91, 95% confidence interval (CI) = 1.22-2.99). Early age at onset (< 46 years) in the relative further increased the risk of developing contralateral breast cancer (sister: multivariable-adjusted RR = 3.36, 95% CI 1.62-6.98; mother: multivariable-adjusted RR = 2.35, 95% CI 1.02-5.43). Bilateral breast cancer in mothers was also associated with more than a two and a half-fold increase in risk (multivariable-adjusted RR = 2.55, 95% CI 1.02-6.35). The association between family history of breast cancer and risk of contralateral breast cancer did not vary substantially according to age at onset of the first primary breast cancer. The age-adjusted rate ratio for development of a second primary breast cancer among women with a first-degree relative with endometrial cancer was 2.13 (95% CI 1.04-4.35), while the corresponding rate ratio among women with a family history of ovarian cancer was 1.69 (95% CI 0.42-6.83). There was little evidence that age at onset among the relatives with endometrial or ovarian cancer affected the risk. Some of these findings have not been previously reported and need replication in future studies.

Risk factors predicting the incidence of second primary breast cancer among women diagnosed with a first primary breast cancer

This study examined risk factors for development of a contralateral breast cancer among 4,660 US women diagnosed with a first primary breast cancer between 1980 and 1982. The authors believe it to be the first prospective cohort study on this topic that has employed direct patient interviews. All subjects were interviewed within 6 months of the diagnosis of their initial tumor as part of the multi-center, population-based, case-control Cancer and Steroid Hormone Study, and they were followed until the end of 1986 through the Surveillance, Epidemiology, and End Results program. Exclusive of those diagnosed during the initial 6 months after diagnosis of a first primary, 136 second primary breast cancers were identified. Proportional hazards models were used to assess the independent effects of multiple predictors. Specific risk factors evaluated included: age at diagnosis of first primary, exposure to exogenous hormones, menstrual and reproductive histories, tumor characteristics, demographic variables, and treatment modalities. The age-specific incidence rates of second primary breast cancer were higher in all age categories than are the incidence rates of breast cancer in the general population, yet the age at diagnosis of first primary breast cancer was not an important predictor of contralateral breast cancer. The risk of contralateral breast cancer was increased among cohort members who reported a personal history of benign breast biopsy (multivariable-adjusted rate ratio (RR) = 1.69, 95% confidence interval (CI) 1.13-2.53) and in those with an initial tumor that was classified as lobular carcinoma (multivariable-adjusted RR = 1.96, 95% CI 1.17-3.27). Treatment with chemotherapy for the first primary was associated with a lower risk of development of a second breast cancer (multivariable-adjusted RR = 0.56, 95% CI 0.33-0.96), while radiation therapy had little effect on the risk (multivariable-adjusted RR = 1.19, 95% CI 0.78-1.80).

Time trends of non-Hodgkin's lymphoma: are they real? What do they mean?

Factors that need to be considered in the analysis of time trends in disease incidence are age, year of diagnosis, and birth cohort. When these are included in a log-linear model, a nonidentifiability problem arises from the linear dependence among these three time factors so that only specified functions of the parameters can be unambiguously determined. One of these invariant functions is the drift or the sum of the period and cohort trend. Non-Hodgkin's lymphoma incidence rates from Connecticut for the period 1935-1989 were analyzed for males and females. In addition to an age effect, both period and cohort significantly improved the fit of the model. The estimated drift shows that there has been a 10.3% increase in risk every 5 years since 1965 for females and 9.2% for males. It is unlikely that a trend of this magnitude can be attributed entirely to data artifact.

Time trend and age-period-cohort effects on incidence of esophageal cancer in Connecticut, 1935-89

The purpose of this study was to examine the incidence pattern of esophageal cancer in Connecticut (USA) during the past decades, and to identify components of birth cohort, period, and and age as determinants of the observed time trends by regression modelling. This study is based on all of the esophageal cancer cases reported to the Connecticut Tumor Registry between 1935 and 1989. A total of 6,310 incident cases were included. Results indicate that among males, the overall age-adjusted incidence rate of esophageal cancer increased after 1935 and peaked between 1955 and 1959. Since then, incidence rates have been relatively stable. Among females, the overall esophageal cancer rate has not changed markedly since 1935. Analysis by histologic type indicates that the incidence rate of squamous cell carcinoma has been declining in this population; adenocarcinoma, however, showed a continuous increase. A fivefold increase among males and a threefold increase among females were observed for adenocarcinoma of the esophagus between 1970 and 1989. If cancers of the esophagus and gastric cardia are considered together, the incidence rate of adenocarcinoma exceeds that of squamous cell carcinoma among males during 1985-89. The observed increasing trend for adenocarcinoma of the esophagus is mainly from cancers arising in the lower third of the esophagus and primarily among Whites, especially White males. The results from regression modeling indicate that both period and birth cohort may have contributed to the observed increasing trend, and adenocarcinoma of the esophagus is likely to increase continuously in this population in the coming years.

Epidemiology of non-Hodgkin lymphoma in Connecticut. 1935-1988

BACKGROUND

During the past decades, there have been reports of increases in the incidence and mortality rates due to non-Hodgkin lymphoma (NHL) in many parts of the world. The risk factors responsible for the increasing incidence are largely unknown. This study provided an overview of the incidence pattern of NHL in Connecticut and generated hypotheses for additional investigation.

METHODS

This study was based on all the NHL cases reported to the Connecticut Tumor Registry (CTR) between 1935 and 1988. Crude, age-adjusted, and age-specific incidence rates of NHL were calculated for each sex. Age-adjusted incidence rates were calculated by the direct method standardized to the 1970 United States standard million population. The data are presented by calendar year and cohort year of birth to examine the secular trends and birth cohort effects. Racial information was not coded before 1957 and is of uncertain validity until the early 1970s; therefore, racial analysis was restricted to 1970-1988. Analyses by histologic subtypes and by anatomic sites were restricted to the last 3 decades (1960-1988) because more accurate classification systems were used during this time.

RESULTS

A total of 11,326 newly diagnosed cases of NHL were included in the study. Of them, 5866 (52%) were diagnosed in men and 5460 (48%) were diagnosed in women. The study results indicated that the incidence rate of NHL has been increasing during the past decades for men and women, whites and blacks, nodular NHL and diffuse NHL, disease originating from lymph nodes and disease originating from other sites, and in all age groups, especially the older age groups. Birth cohort examination did not show any indication of a decline or levelling off in incidence rates among recent birth cohorts. Age-specific incidence rates in both sexes suggested that the rates increase with age, with a sharp increase beginning at 50 years of age and peaking at 80 years of age. Men had a 30% higher incidence rate than women, and whites had approximately 1.5 times the age-adjusted incidence rate of blacks.

CONCLUSIONS

The results indicated that the incidence rate of NHL has been increasing in Connecticut during the past decades and is likely to continue to rise in the coming years. Analytical epidemiologic studies are needed to examine the risk factors that might account for the increase in NHL.

A model for estimating level and net severity of spinal cord injuries

Objective and detailed neurological assessments are essential in studies of the treatment and the epidemiology of acute spinal cord injuries. In practice, investigators use the expanded score, found by taking the total of the individual determinations, but this summary obscures important detail as to the level and the overall severity of injury. To address this issue, we present a method for estimating level and net severity of injury that makes use of isotonic regression and the Spearman-Kärber estimator. We describe the method for both sensory and motor assessments of neurologic function. In the special case where one gives an identical weight to the response at each level, these estimators algebraically partition the expanded score into separate contributions due to level and net severity. We provide a numerical example using data from the first National Acute Spinal Cord Injury Study, and we present a summary of the distribution of these parameters for this population.

A reversal in the long-term increase in deaths attributable to malignant melanoma

For a few years in the 1980s, United States mortality rates suggested a plateau in the long-term increase for malignant melanoma. However, temporary plateaus in the increase of the age-adjusted rate by year of death have occurred in previous decades, only to be followed by a continued upward increase, with a long-term rise of about 2% per year. To determine whether a cessation in the long-term increase might be in progress, death rates were analyzed by year of birth, age at death, and year of death: (1) the long-term patterns of change are best described by birth cohort rather than by time period of death, indicating that analyses by a year of birth are key to a better understanding of the long-term trends; (2) in both men and women, evidence for a change in slope begins among those born in the early 1930s; (3) the decline in the rates begins among women born since the early 1930s and among men born since the early 1950s: the slope for men is -0.2661 (95% confidence limits [CL] = -0.380 to -0.152), and, for women, the slope is -0.02354 (95% CL = -0.041 to -0.005); (4) long-term Connecticut and US mortality trends were similar in pattern and direction, and long-term Connecticut incidence rates showed a persistent increase through the 1955 to 1965 birth cohorts. These analyses suggest a persistent cessation in the long-term increase and a downward trend in death rates from this cancer.

Methylprednisolone or naloxone treatment after acute spinal cord injury: 1-year follow-up data. Results of the second National Acute Spinal Cord Injury Study

The 1-year follow-up data of a multicenter randomized controlled trial of methylprednisolone (30 mg/kg bolus and 5.4 mg/kg/hr for 23 hours) or naloxone (5.4 mg/kg bolus and 4.0 mg/kg/hr for 23 hours) treatment for acute spinal cord injury are reported and compared with placebo results. In patients treated with methylprednisolone within 8 hours of injury, increased recovery of neurological function was seen at 6 weeks and at 6 months and continued to be observed 1 year after injury. For motor function, this difference was statistically significant (p = 0.030), and was found in patients with total sensory and motor loss in the emergency room (p = 0.019) and in those with some preservation of motor and sensory function (p = 0.024). Naloxone-treated patients did not show significantly greater recovery. Patients treated after 8 hours of injury recovered less motor function if receiving methylprednisolone (p = 0.08) or naloxone (p = 0.10) as compared with those given placebo. Complication and mortality rates were similar in either group of treated patients as compared with the placebo group. The authors conclude that treatment with the study dose of methylprednisolone is indicated for acute spinal cord trauma, but only if it can be started within 8 hours of injury.

Cross-cultural association between dietary animal protein and hip fracture: a hypothesis

Age-adjusted female hip fracture incidence has been noted to be higher in industrialized countries than in nonindustrialized countries. A possible explanation that has received little attention is that elevated metabolic acid production associated with a high animal protein diet might lead to chronic bone buffering and bone dissolution. In an attempt to examine this hypothesis, cross-cultural variations in animal protein consumption and hip fracture incidence were examined. When female fracture rates derived from 34 published studies in 16 countries were regressed against estimates of dietary animal protein, a strong, positive association was found. This association could not plausibly be explained by either dietary dietary calcium or total caloric intake. Recent studies suggest that the animal protein-hip fracture association could have a biologically tenable basis. We conclude that further study of the metabolic acid-osteoporosis hypothesis is warranted.

Understanding the effects of age, period, and cohort on incidence and mortality rates

Time trends for population-based disease rates often are summarized by using direct adjustment by period of diagnosis or death. Similarly, the effect of age often is presented graphically as age-specific rates for a given period of diagnosis. These approaches may be necessary if there is an absence of long-term data, as they provide a natural way for annually updating information when monitoring trends, or they may be a convenient way of summarizing a large amount of data (7, 10, 11, 39, 45). However, these summaries only can adjust for the effect of age in a given period; they implicitly ignore the cohort effect. The effect of cohort is an important factor in understanding time trends for many diseases. Thus, it is not advisable to use data analytic strategies that routinely ignore it. Another alternative to modeling is to give a graphical presentation of the age-specific rates themselves. As I noted in the introduction, some of the first analyses to identify the effect of cohort on diseases, such as tuberculosis and lung cancer, relied entirely on a graphical analysis. Although graphs certainly are an important part of the interpretation of time trends, it would be a mistake to limit your analysis to impressions of points on a graph. For example, such a perusal would not give an objective indication of the statistical significance of a particular pattern. Regression analysis forces us to recognize a fundamental problem with interpreting time trends in disease rates--a problem that you should remember, even when trying to understand a graphical display of time trends in age-specific rates.

Trends in female breast cancer in Connecticut and the United States

Trends for female breast cancer were examined by age, period and cohort for the years 1950-1984 in U.S. mortality. Connecticut mortality and Connecticut incidence. Birth cohort patterns were evident for all three sets of data. The results confirm a continuing increase in invasive breast cancer by providing evidence of a strong birth cohort pattern, over a time series of 90 years of birth cohorts. This trend appears to be real for the most part because of the cohort patterns and because there is minimal underdetection in data obtained by autopsy and blind biopsy. Secondly, when cohort modeling is applied to breast cancer mortality, there is an indication of a modest decline in recent breast cancer mortality (in the face of an apparent long-term increase), which suggests that control of breast cancer mortality may have developed in recent decades, perhaps through earlier detection and improved treatment. Finally, in contrast with a prior report, there is little evidence for a clinically important difference in time trend between pre- and postmenopausal breast cancer.

A randomized, controlled trial of methylprednisolone or naloxone in the treatment of acute spinal-cord injury. Results of the Second National Acute Spinal Cord Injury Study

Studies in animals indicate that methylprednisolone and naloxone are both potentially beneficial in acute spinal-cord injury, but whether any treatment is clinically effective remains uncertain. We evaluated the efficacy and safety of methylprednisolone and naloxone in a multicenter randomized, double-blind, placebo-controlled trial in patients with acute spinal-cord injury, 95 percent of whom were treated within 14 hours of injury. Methylprednisolone was given to 162 patients as a bolus of 30 mg per kilogram of body weight, followed by infusion at 5.4 mg per kilogram per hour for 23 hours. Naloxone was given to 154 patients as a bolus of 5.4 mg per kilogram, followed by infusion at 4.0 mg per kilogram per hour for 23 hours. Placebos were given to 171 patients by bolus and infusion. Motor and sensory functions were assessed by systematic neurological examination on admission and six weeks and six months after injury. After six months the patients who were treated with methylprednisolone within eight hours of their injury had significant improvement as compared with those given placebo in motor function (neurologic change scores of 16.0 and 11.2, respectively; P = 0.03) and sensation to pinprick (change scores of 11.4 and 6.6; P = 0.02) and touch (change scores, 8.9 and 4.3; P = 0.03). Benefit from methylprednisolone was seen in patients whose injuries were initially evaluated as neurologically complete, as well as in those believed to have incomplete lesions. The patients treated with naloxone, or with methylprednisolone more than eight hours after their injury, did not differ in their neurologic outcomes from those given placebo. Mortality and major morbidity were similar in all three groups. We conclude that in patients with acute spinal-cord injury, treatment with methylprednisolone in the dose used in this study improves neurologic recovery when the medication is given in the first eight hours. We also conclude that treatment with naloxone in the dose used in this study does not improve neurologic recovery after acute spinal-cord injury.

Conception delay after oral contraceptive use: the effect of estrogen dose

A significant delay was observed in conception among 248 former oral contraceptive (OC) users compared with women discontinuing other methods of contraception (n = 1,365). The mean time to conception was 5.88 cycles (95% confidence interval [CI] 5.38, 6.38) for former OC users and 3.64 cycles (95% CI 3.49, 3.79) after other contraceptives. Women discontinuing OCs with higher doses of estrogen (greater than or equal to 50 micrograms) had greater conception delays than those on lower estrogen doses who, in turn, had longer delays than other method users. Oral contraceptive use was associated with significant reductions in conception for each of the first six cycles after discontinuation. This study provides further evidence for a direct effect of oral contraception on delayed conception, suggests that the delay lasts longer than previously thought, and finds that the probability of conception after OC discontinuation depends on the estrogen dose of the OC.

Log-linear models for the analysis of matched cohort studies

The application of conditional logistic regression to the analysis of matched case-control studies has now become quite customary. In addition, it is well known that software designed to fit linear logistic and log-linear models can be used in these analyses. The application of conditional logistic regression to cohort designs is described, and an approach is developed that adapts the linear logistic and log-linear models for the analysis of prospectively collected data. Specific situations discussed include matched pairs, 2:1 matching, and studies in which some subjects are pair matched and others matched 2:1. The methods are illustrated with numeric examples.

Age, period and cohort effects on the risk of major depression: results from five United States communities

Rates of major depression are presented from the recently completed Epidemiologic Catchment Area (ECA) Study based on probability samples of over 18,000 adults, 18 years of age and older, living in five U.S. communities. These rates were analyzed to describe simultaneously the changes affecting successive birth cohorts and the changes associated with the period in which the onset of the disorder occurred, using age-period-cohort (APC) models. The non-identifiability problem inherent in all APC models was resolved by assuming that the linear period effect and linear cohort effect were non-negative. This assumption is consistent with our a priori substantive knowledge of the disease. Under this assumption, as the linear period effect varies from its minimum to its maximum values, a family of curves representing the possible effects of a factor was generated for each of the time factors--age, period and cohort. The results of the analysis showed a sharp increase in rates of major depression among both men and women in the birth cohort born during the years 1935-1945. The rates among females, however, seemed to have stabilized in the generations born since 1945, while the rates in males continued to rise sharply among the cohorts born in the following decade, after which, in 1955, they also levelled off. In contrast, the rates associated with period of onset of major depression continued to increase between the years 1960-1980 among both men and women of all ages studied. These findings are considered in light of the persistent concentration of depression in women and in biologically related members of families of affected individuals.

Simultaneous interval estimates of the odds ratio in studies with two or more comparisons

More than one odds ratio estimate will often arise from a single epidemiologic study. Examples of designs where this may occur include those where there is more than one case or control group, and investigations of several risk factors as part of the same study. Various methods for presenting multiple interval estimates are discussed, including: the naive method, the Bonferroni method, the Dunn method, the Scheffé method, and the Dunnett method. For rectangular regions the Dunnett method gives a region with the most appropriate confidence level, but this region contains a different set of odds ratio estimates than are implied by the usual significance tests. A confidence ellipse circumscribed by the Scheffé limits gives the best agreement with the significance tests. Each of these methods is illustrated with a numerical example.

Patterns of invasive melanoma in the Connecticut Tumor Registry. Is the long-term increase real?

The decades-long increase in incidence rates for melanoma has been ascribed to artifactual changes in case ascertainment rather than to true changes in disease risk. In this study, population-based incidence data for invasive cutaneous malignant melanoma from the Connecticut Tumor Registry were categorized into seven age groups and four time periods to examine the pattern of change over four decades. Analyses of age, period, and cohort variables focused on the curvature components, which are estimable functions. Statistical modeling demonstrated the following: (1) incidence rates have increased by birth cohort in both sexes with no requirement for a period variable, regardless of whether data are examined by 10-year, 5-year, or 1-year intervals of diagnosis; (2) this pattern in incidence rates differed from the patterns of change in the two indices of case ascertainment, the proportion of cases confirmed microscopically and the proportion of cases in localized stage, both of which exhibited changes by period of diagnosis rather than by birth cohort; and (3) adjustment for these two indices caused a downward bend in the cohort curve for females but not for males. The results suggested that much of the observed increase for this tumor was real.

Exposure to organic solvents and hypertensive disorders of pregnancy

The present investigation compares the frequency of adverse pregnancy complications and outcomes in 90 women who worked with various organic solvents during pregnancy and in 180 unexposed matched (2:1) subjects. Solvent-exposed women were approximately four times more likely to develop preeclampsia, a disorder of pregnancy characterized by hypertension, edema, and proteinuria (unconditional adjusted RR = 3.9, 95% CI = 2.5, 5.4). That hypertension alone, without edema or proteinuria, was also more likely to be reported in solvent-exposed women (unconditional adjusted RR = 3.0, 95% CI = 0.9, 9.9) lent additional support to the association of solvent exposure and hypertensive disorders of pregnancy. Because preeclampsia is thought to be associated primarily with glomerular lesions, our findings, although in need of replication with a larger sample size, may be biologically plausible given the growing literature associating solvent exposure with renal disease. Solvent-exposed women were more likely to have cardiovascular complications and to deliver by cesarean section; however, given the specific type of complications and reason for cesarean, it is unlikely that these findings were directly related to solvent exposure. Other pregnancy complications such as threatened abortion and vaginal bleeding, and poor neonatal growth and maturity, were not more common in the exposed group.

Confounding in epidemiologic studies: the adequacy of the control group as a measure of confounding

A model for confounding in epidemiologic studies is developed based on the adequacy of the "control" group, instead of the widely used criterion of collapsibility, as a measure of confounding. It is shown that conditions for no confounding in both cohort and case-control studies derived under this model generally agree with the conditions for confounding derived inductively by Miettinen and Cook (1981, American Journal of Epidemiology 114, 593-603). The concept of confounding on which this model is based is compared with the collapsibility criterion in terms of its utility in the design and analysis of epidemiologic studies.

Time and age trends for sinonasal cancer in Connecticut incidence and US mortality rates

Population-based rates for sinonasal cancer are examined in US mortality data among whites and in Connecticut incidence data. The observed rates are fitted to a log-linear model in order to examine the effect of each of the three variables, age, period and cohort, simultaneously for each sex. For Connecticut incidence, there is little evidence of either an increase or decrease from 1865 to 1955 birth cohorts. For the US mortality rates, from the 1875 to 1950 birth cohorts, there is a decline by more than twofold in men and more than threefold in women. Monitoring of those trends is discussed with respect to increases in exposure to cigarette smoking and formaldehyde. Regarding the age distribution, both incidence and mortality data are consistent: men show a linear increase of the log (rate) with log (age) in a fashion characteristic of other epithelial nongynecologic malignancies; for women, in contrast, there is a downward curvature around age 50 followed by an upward curvature in the 55 to 70 age range. The rate in most postmenopausal age groups is 20% to 67% of the rate expected on the basis of a linear increase of the log (rate) with log (age). The age patterns in women are similar to "Clemmesen's hook" observed for female breast cancer. There is evidence that the pattern in female subjects differs significantly from that for male subjects. The female age pattern requires confirmation in other populations. An etiologic role for sex hormones is hypothesized in view of that age distribution and in view of physiologic and laboratory observations.

Loss of myeloid differentiation antigens precedes blastic transformation in chronic myelogenous leukemia

In order to determine whether antigenic patterns alter with disease progression and are thereby suggestive of impending blast crisis in chronic myelogenous leukemia, 50 bone marrow biopsy specimens from 32 patients were examined retrospectively using indirect immunoperoxidase labeling with three monoclonal antibodies that detect myeloid antigens. Monoclonal antibodies PMN13F6, PMN7C3, and PMN8C7 detect human neutrophil antigens that first appear at the myeloblast, promyelocyte, and metamyelocyte stages of differentiation, respectively, and persist throughout later differentiation. Percentages of antigen-positive bone marrow cells during the chronic phase were compared with percentages of antigen-positive cells at blast transformation, and time from bone marrow biopsy until blast crisis was correlated with the percentage of bone marrow cells expressing these antigens. Bone marrow biopsy samples from patients in the chronic phase who continue to remain clinically stable 4 to 106 months after biopsy expressed PMN13F6 antigen on 82% +/- 9% (mean +/- SD) of cells, PMN7C3 antigen on 62% +/- 14% of cells, and PMN8C7 on 68% +/- 14% of cells. Bone marrow biopsy specimens obtained from patients 1 or more years prior to blast transformation expressed PMN13F6 antigen on 81% +/- 12%, PMN7C3 antigen on 71% +/- 16%, and PMN8C7 on 64% +/- 16% of cells. Bone marrow biopsy samples obtained between 2 months and 1 year prior to blast crisis expressed PMN13F6 antigen on 68% +/- 15%, PMN7C3 on 51% +/- 17%, and PMN8C7 antigen on 46% +/- 18% of cells. Bone marrow biopsy specimens taken at the time of blast transformation expressed PMN13F6 antigen on 20% +/- 25%, PMN7C3 antigen on 19% +/- 25%, and PMN8C7 antigen on 13% +/- 25% of cells. The difference between the mean of antigen-positive cells from bone marrow biopsy samples obtained at the time of blast crisis was significant compared with the mean of positive cells from biopsy specimens obtained at all other phases of the disease (P less than .001 for all three antibodies). There was a positive correlation between loss of myeloid antigens and disease progression as determined by simple regression of log time and correlation analysis (PMN13F6, r = .6533, P less than .005; PMN7C8, r = .6304, P less than .005; PMN8C7, r = .5215, P less than .05). There was a negative correlation between percentage of immature cells and time to blastic crisis (r = -.6206, P less than .005).(ABSTRACT TRUNCATED AT 250 WORDS)

Risk of late first and second trimester miscarriage after induced abortion

A cohort of 3110 women anticipating delivery were interviewed after their first prenatal visit at private obstetric practices and HMOs in Connecticut. In all 19.57% reported a prior induced abortion. The research participants were followed to determine whether the pregnancy was miscarried or delivered. In all, 2.19% miscarried in the late first or second trimester. The association of a prior induced abortion on risk for late miscarriage was analyzed by pregnancy history. Women who aborted their first pregnancy had no increased risk (RR = 0.56, 95% CI = 0.16, 1.92) of miscarriage compared with women pregnant for the first time, or compared with women experiencing their second pregnancy after delivering the first (RR = 0.69, 95% CI = 0.18, 2.60). No evidence was found for an increased risk of multiple induced abortion on subsequent miscarriage.

Prognostic indicators in diffuse large-cell (histiocytic) lymphoma

Identification of prognostic groups among patients with diffuse large-cell (histiocytic) lymphoma (DHL) would help to select specific therapy for individual patients and allow comparisons among combination chemotherapy clinical trials. The Ann Arbor staging system is of limited value in predicting outcome in diffuse histiocytic lymphoma. Prognostic factors have been examined by various groups without a consensus of reliable prognostic indicators. This study was undertaken to examine the validity of a predictive model for response to treatment and survival in DHL. Eighty-six patients with the diagnosis of DHL treated with combination chemotherapy between the years 1976 and 1982 were examined for prognostic variables influencing response to treatment and survival. The variables examined included: age, sex, presence or absence of systemic symptoms, serum lactic dehydrogenase (LDH), sites of disease involvement, bulk of disease, prior therapy, stage of disease, according to the Ann Arbor classification, and pathological criteria, according to the Lukes Collins classification. Factors achieving a p-value in the 0 to 0.05 range with univariate analysis for predicting response were age and systemic symptoms. Factors significant for overall survival were age and bone marrow involvement. These factors have been found to influence survival in previous studies, but there has not been a consistency regarding the importance of these factors. Large numbers of patients must be examined for various factors in order to allow identification of prognostic groups among patients with DHL.

Low birth weight in pregnancies following induced abortion: no evidence for an association

Compared with women delivering a first pregnancy, those delivering a second pregnancy after aborting the first have similar rates of low (less than 2,500 g) birth weight newborns (relative risk (RR) G2A1/G1 = 0.86, 95% confidence interval (CI) = 0.49-1.51) and mean birth weight (delta = 16.3 g, p = 0.63). Abortion of the first pregnancy prevents the reduction in low birth weight and increase in mean birth weight in the second pregnancy which delivery of the first pregnancy normally bestows (RR G2P1/G2A1 = 0.48, 95% CI = 0.25-0.90; delta = 135.3 g, p less than 0.0001). Two prior induced abortions do not significantly increase risk for low birth weight (RR G3A2/G1 = 1.14, 95% CI = 0.37-3.56) or decrease mean birth weight (delta = 29.0 g), compared with women delivering their first pregnancy. The second of two deliveries has a reduced risk of low birth weight irrespective of whether both deliveries follow an aborted first pregnancy. Adjustment for confounding factors did not materially change these results. Low birth weight rates were higher after abortions performed in hospital compared with elsewhere (p = 0.03), but mean birth weight was not affected. Gestation at abortion, vacuum aspiration or dilatation and curettage, and abortion complications were unrelated to birth weight of subsequent pregnancies. Pregnancies conceived within six months of a prior abortion or delivery had lower birth weight than if the antecedent pregnancy ended more than six months previously.

Long-term prognosis of infertile couples with normal basic investigations: a life-table analysis

The long-term prognosis of 58 untreated infertile couples with normal medical histories and physical examinations, and normal basic infertility investigations, including biphasic basal body temperature, hysterosalpingogram, postcoital test, and semen analysis, was studied using life-table analysis. Of these women, 34% were pregnant by six months, 76% by two years, and 87% by five years. These rates of conception were found to be significantly higher than those found in a large infertile population (P = .001). However, compared with the ideal fertile population, the study group for the first two years had a significantly lower conception rate (P = .001). It required two years for the study group to achieve a 74% fertility rate, whereas only nine months were required for the fertile group to achieve the same rate. The individualized approach for investigating the infertile couple is stressed.

Risk factors for fibrocystic breast disease and its histopathologic components

The relationship between various sociodemographic, reproductive, and other factors to the occurrence of fibrocystic breast disease was evaluated in a case-control study undertaken at five Connecticut hospitals from 1979 to 1981. The study groups comprised 590 women with biopsy-proven fibrocystic breast disease and 1,018 women with other surgical conditions. Among the premenopausal women, multivariate analysis suggested that high socioeconomic status, Jewish religion, low parity, a history of benign breast disease, a history of breast cancer in the mother or a sister, and low Quetelet index were associated with increased odds ratios (OR) for fibrocystic breast disease. Similar analysis for the postmenopausal women revealed increased OR for women with high socioeconomic status, a late age at menopause, and a history of benign breast disease. Current smokers as well as those who had had a tubal sterilization had significantly reduced odds of fibrocystic disease. There was no convincing evidence of linear trends according to degree of epithelial atypia for any of the variables considered. Although some variation in the OR emerged in the analysis according to selected histologic components, the results provided little evidence that women with biopsy specimens exhibiting gross cysts, sclerosing adenosis, papillary hyperplasia, or papillomatosis showed epidemiologic similarities with breast cancer patients.

Risk for cutaneous melanoma in recent Connecticut birth cohorts

Mortality trends suggest that increases in Connecticut incidence for cutaneous melanoma (CM) equal or under estimate increases for the entire country. One-sixth of CM in Connecticut occurs under age 35. In the 1955 birth cohort, modeled incidence rates per 100,000 age-adjusted to the 1960 US population are 38.2 in males and 28.9 in females. These estimated rates for CM rival those for colon cancer (now the third most common malignancy in the United States) and have special implications for young adults.

Time period compared to birth cohort in Connecticut incidence rates for twenty-five malignant neoplasms

Out of necessity and convenience many reports on population-based rates for cancer are limited to analyses by time period of diagnosis, and just how often cohort effects are important in cancer data has not been fully explored. To address this question, Connecticut cancer incidence rates for the years 1940-79 were fitted to the model: Log (incidence rate) = constant + age effect + period effect + birth cohort effect + error term. Data for each cancer site and sex were categorized into 10-year intervals by time period and age group. Significance testing for the curvilinear effects (which are estimable functions) of age (A), period (P), and cohort (C) in the 44 data sets led to no clear choice of model for three data sets; an APC model for 20, an AP model for 7, and an AC model for 14. These choices were corroborated by the RA2 index. Limitations in the interpretation of the results were enumerated. Presentation of population-based cancer rates by implicitly assuming an AP model is valuable (e.g., for studying age distribution in different regions or for age-adjustment in examining international variation or time trends). However, the assumption of an AP model may often be incorrect, as was shown to be the case for most of these 44 data sets. The implications for monitoring trends and generating etiologic hypotheses were discussed in light of the results for cutaneous malignant melanoma and cancers of the cervix, breast, ovary, lung, and bladder.

An epidemiologic study of fibrocystic breast disease with reference to ductal epithelial atypia

A case-control study of 255 women with fibrocystic breast lesions and 790 controls was conducted at two hospitals in New Haven, Connecticut during 1977-1979. Cases were found to weigh significantly less than controls, and were more likely than controls to have: a first-degree female relative with a history of breast cancer; a higher level of education; a recent history of regular gynecologic checkups; and (if under age 45 years) a later age at first pregnancy. They were less likely to have had a surgical menopause. The degree of ductal epithelial atypia in breast biopsy specimens was evaluated in order to see whether epidemiologic characteristics differed according to the degree of ductal atypia. The only variable to show a linear relationship with ductal atypia was a recent history of regular gynecologic checkups; those with no or minimal atypia were more likely to have had recent checkups than those with high atypia scores. This study thus gives no evidence that known risk factors for breast cancer are more strongly associated with fibrocystic breast disease with a high degree of atypia than with fibrocystic breast disease with a low degree of atypia. It also provides data to support the belief that women having frequent gynecologic checkups are more likely to be included as cases in case-control studies of fibrocystic breast disease, and particularly in the groups with no or minimal atypia, than those not having frequent checkups.

Estimation of DNA fragment size and generation of DNA restriction endonuclease maps using linear models

A method for the estimation of DNA fragment size and for the generation of DNA restriction endonuclease maps using linear models is discussed, and a computer program which utilizes the SAS (SAS Institute Inc., 1982) statistical package is presented.

Estrogen replacement therapy and fibrocystic breast disease in postmenopausal women

The association between estrogen replacement therapy and fibrocystic breast disease was assessed in a hospital-based case-control study undertaken in Connecticut from 1979 to 1981. The cases were 143 postmenopausal women with biopsy-confirmed fibrocystic breast disease, and the controls were 355 postmenopausal women with other surgical conditions. Use of estrogen replacement therapy was positively associated with fibrocystic breast disease; the odds of disease increased with duration of use, reaching an approximately fivefold excess odds for those who had taken menopausal estrogens for 10 or more years. There was no evidence that the positive association between estrogen replacement therapy and the occurrence of fibrocystic breast disease could be explained by differential medical care utilization or other possible risk factors of biopsied fibrocystic breast disease.

An alternative approach to statistical age-period-cohort analysis

Age-period-cohort analysis has generated considerable interest in epidemiology, but the model has fundamental problems which have been discussed by Kupper et al. While one can agree that the age-period-cohort model should be used with caution, it should also be noted that some useful inferences can be made with the model. The problems raised by Kupper et al. are discussed in terms of estimable functions of the parameters, which are not affected by arbitrary constraints on the parameters. The use of these methods are illustrated and specific examples presented where age-period-cohort models can be used effectively.

Exogenous hormone use and fibrocystic breast disease by histopathologic component

In a hospital-based case-control study of 590 women with biopsy-proven fibrocystic breast disease and 1,018 control women with other surgical conditions, no linear relationship was evident between the use of oral contraceptives or of estrogen replacement therapy and the degree of epithelial atypia of the fibrocystic lesions. Case-control and intracase comparisons suggested that oral contraceptive use might be associated with an increased occurrence of sclerosing adenosis among the premenopausal women and of gross cysts among the postmenopausal women. Estrogen replacement therapy, which was positively associated with fibrocystic breast disease as a whole among the post-menopausal women, was most frequently used among the cases whose biopsy specimens exhibited gross cysts, papillomatosis or papillary hyperplasia.

Acute prolapsed lumbar intervertebral disc. An epidemiologic study with special reference to driving automobiles and cigarette smoking

An epidemiologic case-control study to identify risk factors for acute prolapsed lumbar intervertebral disc was undertaken in Connecticut during 1979-1981. This paper focuses on nonoccupational factors of possible etiologic significance. Persons in their 30s were affected most frequently. Among surgical cases, the ratio of men to women was 1.5 to 1, while among probable and possible cases not undergoing surgery, the male to female ratio was about 1 to 1. Cigarette smoking in the past year was associated with an increased risk for prolapsed disc. The greater the number of hours spent in a motor vehicle, the higher the risk. Use of Swedish and Japanese cars was associated with a lower-than-average risk, while use of other cars was associated with a higher-than-average risk. For each type of car, older cars were associated with higher risks than newer cars. Variables that did not affect the risk for prolapsed lumbar disc in this study included height, weight, number of pregnancies, number of children, frequency of wearing shoes with high heels, smoking cigars or pipes, and participation in baseball or softball, golf, bowling, swimming, diving from a board, tennis, bicycling or jogging.

An epidemiological study of acute prolapsed cervical intervertebral disc

In this epidemiological study of acute prolapsed cervical intervertebral disc, we found that people in the fourth decade of life were affected somewhat more frequently than individuals in other age groups, and men with a prolapsed cervical disc outnumbered women by a ratio of 1.4 to one. Factors that were associated relatively strongly with this diagnosis were frequent lifting of heavy objects on the job that was held around the time of the onset of symptoms, cigarette-smoking, and frequent diving from a board. Positive associations that were of borderline statistical significance or were not statistically significant were found with operating or driving vibrating equipment and time spent in motor vehicles. Variables that did not appear to affect the risk for a prolapsed cervical disc included participation in certain sports other than diving, frequent wearing of shoes with high heels, the number of pregnancies or live births, frequent twisting of the neck on the job, time spent sitting on the job, and smoking cigars or a pipe.

Oral contraceptive use and fibrocystic breast disease among pre- and postmenopausal women

The association between use of oral contraceptives and fibrocystic breast disease was assessed among women aged 20-74 years in a hospital-based case-control study conducted between November 1979 and November 1981 in Connecticut. The study groups comprised 633 women with biopsy-proven fibrocystic breast disease and 1,062 controls who had been admitted, as inpatients or outpatients, to general surgical services. For the premenopausal women, there was no evidence that long-term use of oral contraceptives was associated with a decreased frequency of fibrocystic breast disease among either current or past users. For the postmenopausal women, previous oral contraceptive exposure was associated with an increased occurrence of cystic disease. These findings contradict previous investigations reporting a negative association between oral contraceptive use and the development of fibrocystic breast disease.

An epidemiologic study of lifting and twisting on the job and risk for acute prolapsed lumbar intervertebral disc

An epidemiologic case-control study undertaken in Connecticut during 1979-1981 indicated that persons with jobs requiring lifting objects of more than 11.3 kg (25 lb) an average of more than 25 times per day had over three times the risk for acute prolapsed lumbar intervertebral disc as people whose jobs did not involve lifting objects of this weight. If the body was usually twisted while the lifting was done, this elevation in risk was apparent with less frequent lifting. An especially high risk for prolapsed lumbar disc was associated with jobs involving lifting objects of more than 11.3 kg with the body usually twisted and the knees not bent while the lifting was done. Neither lifting objects of less than 11.3 kg nor twisting without lifting was associated with an increase in risk.

Physical activity and the risk of spontaneous preterm delivery

An epidemiologic case-control study exploring possible risk factors for preterm delivery was undertaken at Yale-New Haven Hospital during 1977. The study groups consisted of 175 mothers of singleton preterm infants and 313 mothers of singleton term infants. Analysis of questionnaire responses provided no evidence that employment, housework, child care and leisure-time physical activity during pregnancy increased the risk of preterm delivery. Women who participated in sports or physical fitness exercises during pregnancy were found to have a significantly decreased risk of preterm delivery as compared to those who were not similarly active; this finding suggests that certain forms of moderate physical activity may actually protect against preterm delivery.

Oral contraceptive use and fibrocystic breast disease with special reference to its histopathology

The relationship between use of oral contraceptives and fibrocystic breast disease was examined in a hospital-based case-control study undertaken in New Haven, Connecticut, from 1977 to 1979. Particular emphasis was placed on the extent of epithelial atypia and other histopathologic characteristics found in the biopsy specimens from the cases. Women who had ever used oral contraceptives were at a somewhat decreased risk for fibrocystic disease as a whole. Cases with high atypia and controls had similar patterns of oral contraceptive use, whereas cases with low and intermediate atypia had less oral contraceptive use than controls. Cases with intermediate atypia reported the lowest oral contraceptive use. Subjects with biopsy specimens exhibiting gross cysts, microscopic cysts, or papillomatosis were about 50% less likely to have used oral contraceptives than controls.