The internal clock: evidence for a temporal oscillator underlying time perception with some estimates of its characteristic frequency

Evidence for the proposition that human time perception is determined by an internal clock is largely indirect. It would strengthen the case for this hypothesis if a model for the internal clock were available from which predictions could be derived and tested, and if the basic parameter of such a model, the frequency at which the clock runs, could be estimated. A model for an internal temporal pacemaker is briefly described and its properties are explored by computer simulation. Results are obtained that provide a basis for predicting that, under appropriate conditions, interference between an imposed rhythm and the frequency of a temporal oscillator may cause perturbations in temporal judgment which are related to the characteristic frequency of that oscillator. Experimental data are reported which appear to demonstrate such an interference pattern. These results allow some estimates of the characteristic frequency of the temporal oscillator to be obtained.

The NIMH Methods for the Epidemiology of Child and Adolescent Mental Disorders (MECA) Study: background and methodology

OBJECTIVE

A collaborative study was conducted to develop methods for surveys of mental disorder and service utilization in unscreened population-based samples of children and adolescents.

METHOD

Probability household samples of youths 9 through 17 years of age were selected at four sites and interviews were conducted with a total of 1,285 pairs of youths and their adult caretakers in their homes. Lay interviewers administered a computer-assisted version of the NIMH Diagnostic Interview Schedule for Children Version 2.3 and structured interviews to assess demographic variables, functional impairment, risk factors, service utilization, and barriers to service utilization.

RESULTS

More than 7,500 households were enumerated at four sites, with enumeration response rates above 99%. Across sites, 84% of eligible youth-caretaker pairs were interviewed for about 2 hours each. Ninety-five percent of both youths and caretakers found the interview to be acceptable enough to recommend to a friend.

CONCLUSIONS

These findings indicate that large-scale epidemiological surveys of mental disorders and mental health service use involving lengthy interviews in the homes of unscreened population-based samples of youths and their adult caretakers are acceptable to the community and can achieve good response rates. The other reports in this Special Section address the reliability and validity of the various survey instruments and other key findings.

The nucleus basalis of Meynert in neurological disease: a quantitative morphological study

The recent finding of neuronal degeneration in the nucleus basalis of Meynert (nbM) in Alzheimer's disease suggests a possible role of this nucleus and the cholinergic system in dementing illness. We assessed neuronal population and density in two anatomical levels of the nbM in 38 coded brains from patients with a broad variety of neurological disorders. We found the most striking nbM degeneration in Alzheimer's and Parkinson's diseases. An intermediate loss of neurons was noted in the transmissible dementia Creutzfeldt-Jakob disease and in progressive supranuclear palsy. The usually nondementing diseases amyotrophic lateral sclerosis and multiple sclerosis showed cell counts comparable to those in a control group of nondemented patients with cerebrovascular disease. Characteristic neuropathological changes of Alzheimer's, Parkinson's, and Creutzfeldt-Jakob diseases, progressive supranuclear palsy, and subacute sclerosing panencephalitis were also found in the nbM. Most previous studies of the nbM have been based on small numbers of cases compared with controls. In our large series we used consistent methodology and a multiple-comparison statistical procedure to avoid overreporting of statistical significance. Our comparison of the nbM not only confirms the marked degeneration of the nbM in Alzheimer's disease, but also places such degeneration into perspective in a spectrum of dementing and nondementing neurological diseases. Larger case studies, using appropriate statistical techniques for multiple group comparisons, are needed to establish the significance of nbM degeneration in neurological disease.

Prevalence and correlates of harassment among US women physicians

BACKGROUND

Despite concerns about its prevalence and ramifications, harassment has not been well quantified among physicians. Previous published studies have been small, have surveyed only 1 site or a convenience sample, and have suffered from selection bias.

METHODS

Our database is the Women Physicians' Health Study, a large (4501 respondents; response rate, 59%), nationally distributed questionnaire study. We analyzed responses concerning gender-based and sexual harassment.

RESULTS

Overall, 47.7% of women physicians reported ever experiencing gender-based harassment, and 36.9% reported sexual harassment. Harassment was more common while in medical school (31% of gender-based and 20% for sexual harassment) or during internship, residency, or fellowship (29% for gender-based and 19% for sexual harassment) than in practice (25% for gender-based and 11% for sexual harassment). Respondents more likely to report gender-based harassment were physicians who were now divorced or separated and those specializing in historically male specialties, whereas those of Asian and other (nonwhite, nonblack, non-Asian, non-Hispanic) ethnicity, those living in the East, and those self-characterized as politically very conservative were less likely to report gender-based harassment. Being younger, born in the United States, or divorced or separated were correlated with reporting ever experiencing sexual harassment; those who were Asian or who were currently working in group or government settings were less likely to report it. Those who felt in control of their work environments, were satisfied with their careers, and would choose again to become physicians reported lower prevalences of ever experiencing harassment. Those with histories of depression or suicide attempts were more likely to report ever having been harassed.

CONCLUSIONS

Women physicians commonly perceive that they have been harassed. Experiences of and sensitivity to harassment differ among individuals, and there may be substantial professional and personal consequences of harassment. Since reported rates of sexual harassment are higher among younger physicians, the situation may not be improving.

Prenatal and perinatal risk factors for breast cancer in young women

There is increasing interest in the role of early life exposures in breast carcinogenesis, especially estrogen exposure in utero. Estrogen levels during pregnancy may be higher in twin pregnancies and among older women and slightly lower among smokers. We analyzed early life risk factors in a population-based case-control study in the United States of 2,202 breast cancer cases and 2,009 controls under age 55 years. Twins were at an increased risk of breast cancer compared with singletons (relative risk = 1.62; 95% confidence interval = 1.0-2.7), particularly women with a twin brother (relative risk = 2.06), a finding consistent with the observation of high estrogen levels in dizygotic twin pregnancies. Little association was seen between maternal age at birth and breast cancer risk. We carried out further analyses for 534 cases and 497 controls under age 45 years, using data from a questionnaire completed by their mothers relating to the daughters' early life exposures. There was no evidence of an effect of smoking or diethylstilbestrol exposure during pregnancy on daughters' breast cancer risk. A reduced breast cancer risk was seen among women who had been breastfed (relative risk = 0.74; 95% confidence interval = 0.6-1.0). These findings indicate some effect of early life exposures on breast cancer risk, although the role of estrogen exposure may be less central than previously suggested.

Breast cancer risk in young women and history of selected medical conditions

BACKGROUND

Several common medical conditions are associated with altered hormone levels, and may thus plausibly influence breast cancer risk. Few studies have examined such relationships, and we utilized a population-based case-control study of young women in the US to examine breast cancer risk following a history of various medical conditions. Relationships between breast cancer and each medical condition examined are biologically plausible, and relevant in terms of public health.

METHODS

The study included 2173 breast cancer cases and 1990 population-based controls from three areas of the US, under 55 years, who were administered a questionnaire including details of physician-diagnosed medical conditions.

RESULTS

No significantly increased or decreased breast cancer risk was associated with a history of thyroid disease, gallbladder disease, colorectal polyps, diabetes, high blood pressure, high cholesterol or surgery for endometriosis. There was some evidence of an increased breast cancer risk associated with ovarian cysts among women who did not receive an oophorectomy (relative risk [RR] = 1.94, 95% CI: 1.0-3.9). Non-significant increases in breast cancer risk were observed following diagnoses of several other cancers, including thyroid cancer, basal cell carcinoma, Hodgkin's disease and malignant melanoma.

CONCLUSIONS

To conclude, our generally null results from this large, population-based study support results from previous studies in providing reassurance that women with a history of several common medical conditions do not appear to be at an increased risk of breast cancer at a young age.

Financial cost as an obstacle to hypertension therapy

A home health interview, including blood pressure measurements, was conducted on 4,688 adults representing the noninstitutionalized population of Georgia. Subjects with diastolic blood pressure greater than or equal to 90 mm Hg or on antihypertensive medication were considered hypertensive. The prevalence of uncontrolled moderate or severe hypertension (diastolic greater than or equal to 105 mm Hg) was 1.9 per cent. With the exception of White women, all race-sex groups with uncontrolled moderate or severe hypertension reported substantially lower per capita income than their mild or controlled hypertensive counterparts. A larger percentage of the uncontrolled moderate to severe hypertensives on medication, as compared to their mild or controlled counterparts, reported economic barriers to pharmacologic and medical care on cost of medicines (36 per cent vs 22 per cent); refills (36 per cent vs 16 per cent); and office visits (26 per cent vs 16 per cent). Black women reported these barriers more than Whites. These findings suggest that costs of antihypertensive care may be an obstacle in blood pressure control for certain population subgroups.

Epidemiology of in situ and invasive breast cancer in women aged under 45

The incidence of in situ breast cancer in the USA has increased rapidly in recent years, even among young women. A population-based case-control study of 1616 breast cancer cases aged under 45 in the USA was used to examine risk factors for in situ, local and regional/distant tumours. Almost 60% of in situ tumours were detected by routine mammograms compared with 18% of local tumours and 8% of regional/distant tumours. After adjustment for screening history and established risk factors, family history of breast cancer in a first-degree relative and African-American race were associated with an increased risk of all stages of breast cancer. The associations with nulliparity, a previous breast biopsy and body mass index were significantly stronger for in situ tumours than for local or regional/distant disease. Alcohol consumption was associated with an increasing trend in risk of regional/distant tumours but not of earlier stage tumours, indicating that alcohol may be involved in late-stage events. Analyses by histological type of in situ tumours suggested that both ductal and lobular carcinoma in situ were associated with most established breast cancer risk factors, and the magnitude of association tended to be greater for the ductal form.

Diet during adolescence and risk of breast cancer among young women

BACKGROUND

A variety of breast cancer risk factors pertain to a woman's adolescence and may be related to nutritional influences. We assessed risk of early-onset breast cancer related to diet during adolescence in a case-control study.

METHODS

Study participants were accrued from the following three geographical regions covered by cancer registries: Atlanta, GA; Seattle/Puget Sound, WA; and central New Jersey. Case patients (n = 1647) were newly diagnosed with breast cancer, and control subjects (n = 1501) were identified by random-digit-dialing techniques. In an interview, each subject was asked to recall the frequency of consumption and portion size of 29 key food items at ages 12-13 years. Mothers of a subset of respondents completed questionnaires, and food groups were recalculated after removal of foods with poor agreement between mother and daughter. Logistic regression analyses were used to calculate odds ratios and 95% confidence intervals.

RESULTS

When high versus low quartiles of consumption were compared, there was a suggestion of a reduced risk associated with high consumption of fruits and vegetables, although this finding was not statistically significant. Slight increases (of borderline statistical significance) in risk of breast cancer were found for intake of chicken or high-fat meat. Intake of animal fat, high-fat foods, high-fat snacks and desserts, or dairy products during adolescence had no apparent influence on breast cancer risk. Removal of foods suspected to be poorly recalled by the daughters did not change any of the risk estimates.

CONCLUSION

These data do not provide evidence for a strong influence of dietary intakes during adolescence on risk of early-onset breast cancer.

The Pregnancy Risk Assessment Monitoring System: design, questionnaire, data collection and response rates. PRAMS Working Group

The birth certificate, the primary tool for population-based surveillance of the condition of infants at birth and maternal status during pregnancy, provides little data about maternal behaviour during pregnancy. To collect data on maternal behaviours that influence pregnancy outcome, we implemented the Pregnancy Risk Assessment Monitoring System in seven states. For this population-based surveillance, new mothers were sampled from birth certificates 2 to 6 months after delivery and contacted by mail; follow-up of nonrespondents was by telephone. Participants completed a 10-page questionnaire. Stratification permitted over-sampling of women with adverse pregnancy outcomes. Among 10,563 women sampled during 1988 and 1989, stratum-specific response rates ranged from 30% to 89%. In 11 of the 28 strata, response rates were greater than 70%. Response rates varied considerably between states. Rates were lower for Black mothers, mothers of low birthweight infants, unmarried mothers and mothers with less than 12 years of education. Active refusal to participate and undelivered mail occurred infrequently. Mail and telephone surveillance of new mothers can yield adequate response rates in selected population groups. Trials of alternative approaches to enhancing response among Black and disadvantaged mothers, such as additional mailings or post-partum in-hospital recruitment, are needed.

Recreational physical activity and breast cancer risk among women under age 45 years

To evaluate whether recreational physical activity is associated with breast cancer among young women, the authors analyzed data from a population-based case-control study. Cases (n = 1,668) were women under age 45 years who had been newly diagnosed with breast cancer between 1990 and 1992 in Atlanta, Georgia, central New Jersey, or Seattle, Washington. Controls (n = 1,505) were frequency-matched to cases by 5-year age group and geographic area of residence. Breast cancer was not associated with recreational activity in any of the three time periods assessed (highest quartile of activity vs. lowest: age- and center-adjusted odds ratio (OR) = 0.94 (95% confidence interval (CI) 0.77-1.15) at ages 12-13 years, OR = 1.08 (95% CI 0.88-1.32) at age 20 years, and OR = 1.18 (95% CI 0.97-1.44) during the past year), with the average of the three time periods (OR = 1.02, 95% CI 0.84-1.25), or with daily climbing of at least two flights of stairs (without stopping) during the past year (daily climbing vs. never climbing: OR = 1.03, 95% CI 0.86-1.23). Estimates were not modified or confounded by body mass index, menopausal status, or caloric intake during the past year. These results do not support a protective role for physical activity in the risk of breast cancer among young women.

Increasing the accuracy of the Expanded Programme on Immunization's cluster survey design

The Expanded Programme on Immunization (EPI) of the World Health Organization developed a cluster survey design for the rapid assessment of children's vaccination coverage in developing countries. Because of its simplicity and familiarity, the EPI methodology has been used for additional purposes, including the detection of relatively small changes in vaccination coverage levels that are already high and the estimation of other population parameters when moderate accuracy is required. This article suggests techniques for improving the accuracy of the EPI cluster survey method, including (a) segmenting sample clusters, if necessary, so that reasonably sized areas can be counted, mapped, and listed; (b) selecting an equal probability sample of housing units within a cluster; (c) selecting a fixed number of housing units per sample cluster; and (d) performing weighted analyses. These procedures will produce accurate estimators and corresponding standard errors in EPI cluster surveys.

Stage of breast cancer in relation to body mass index and bra cup size

Most studies on women with breast cancer indicate that obesity is positively associated with late-stage disease. Some results have shown a similar relationship between breast size and stage. A recent study found that the association between body mass index (BMI) and stage was limited to cancers that were self-detected, suggesting that the BMI-stage relation may be due to delayed symptom recognition. We examined the relationships between stage and both BMI and breast (bra cup) size, stratified by method of detection, using data from a population-based case-control study of 1,361 women (ages 20-44 years) diagnosed with breast cancer during 1990-1992. Height and weight measurements and information on bra cup size, method of cancer detection and other factors predictive of stage at diagnosis were collected during in-person interviews. A case-case comparison was conducted using logistic regression to estimate odds of regional or distant stage rather than local stage in relation to BMI and bra size. Odds of late-stage disease were increased with higher BMI [adjusted odds ratio (OR) for highest to lowest tertile = 1.46, 95% confidence interval (CI) 1.10-1.93] and larger bra cup size (OR for cup D vs. cup A = 1.61, 95% CI 1.04-2.48). These relationships were not modified by the method of detection. Differences in etiologic effects, rather than differences in detection methods, may explain the relations observed between stage and both BMI and breast size.

End-stage renal disease treatment modality and patients' quality of life. Longitudinal assessment

Quality of life assessments were obtained at two 18-month follow-up intervals from 97 end-stage renal disease patients. Data were compared for three stable treatment groups (transplant, home hemodialysis, in-center hemodialysis) and for two transfer treatment groups (hemodialysis to transplant, hemodialysis to continuous ambulatory peritoneal dialysis). Home hemodialysis patients demonstrated the highest quality of life and lowest hospitalization rates over time. Transplant patients had higher employment and perceived health status but not necessarily higher subjective quality of life as compared to in-center hemodialysis patients, and transplant patients experienced more hospitalization. At follow-up, hemodialysis patients who obtained transplants assessed their quality of life as higher than did hemodialysis patients who went on continuous ambulatory peritoneal dialysis.

The spatial signal for saccadic eye movements emphasizes visual boundaries

By investigating the visual processing involved when saccades are made to newly appearing targets, we show that this processing is significantly nonlinear and that texture boundary information predominates. We used the global, or center-of-gravity, effect whereby a saccadic eye movement directed to a target consisting of a pair of elements has an amplitude intermediate between that of saccades directed to the individual elements. We measured the effect using target elements with different visual characteristics, including phase-reversal checkerboard targets that had the same space-average luminance as the background. The contribution to the center-of-gravity calculation was used to measure relative salience. We found that positive and negative contrast elements contribute almost equal weightings. Thus, salience, assessed in this way, is a highly nonlinear function of luminance. The salience of checkerboard targets was found to decrease as check size was decreased and increase as the overall size of the target was increased. Checkerboards with an empty center were as effective as were full checkerboards, showing the importance of boundaries in the salience signal.

Continued survival of older hemodialysis patients: investigation of psychosocial predictors

This study investigated whether social and/or psychologic factors help to predict older dialysis patients' continued survival. A stratified (by race and sex) random sample of patients aged 60+ years was selected from the ESRD Network census of all patients in that age category residing in a single southeastern state (Georgia) and receiving chronic dialysis as of November 1987; personal interviews with patients were completed in 1988. This analysis includes 287 patients (mean age, 69 years) receiving outpatient hemodialysis for whom primary cause of renal failure and functional status data were complete. Patient tracking and vital statistics data determined that 49% of the sample survived as of October 31, 1990. Study variables included demographic, dialysis, health status, social situation, and psychologic outlook variables reported at the patients' 1988 interviews. Log rank tests showed univariate associations between patients' continued survival and race/gender, recovery time following dialysis treatments, cardiovascular co-morbidity, exercise activity score, freedom from health limitation of daily activity, functional status, leisure activity score, self-rated health status, overall life satisfaction, depression, and public religiosity. The Cox proportional hazards model was fit to the data, with continued survival from the time of the 1988 interview as the dependent variable. There was a significantly increased mortality risk for white men relative to the other race/gender groups and for patients reporting severely impaired functional status at the 1988 interview. With functional status in the model, no other social or psychologic variables were significant predictors of mortality.(ABSTRACT TRUNCATED AT 250 WORDS)

Employment status and ability to work among working-age chronic dialysis patients

283 patients, age 18-59 years on chronic dialysis were interviewed about their current work status and their ability to work if currently not employed. Only 11% of the total sample was currently employed. However, one third of the nonemployed patients said they were able to work, and most of these patients had made an effort to be employed. Age, race, educational level, health status, and physical ability to perform job tasks, recent work experience, and interest in working were related to the reported ability to work. Patients who said they were able to work were also likely to be rated able to work by the medical director of their dialysis facility. The data indicate the importance of helping work-interested patients maintain their jobs when they start chronic dialysis treatment.

Characteristics of respondents and non-respondents from a case-control study of breast cancer in younger women

BACKGROUND

This study assessed the nature of potential biases by comparing respondents with non-respondents from a case-control study of breast cancer in younger women.

METHODS

The case-control study was conducted in three regions in the US: Atlanta GA, Seattle/Puget Sound WA, and central New Jersey. An abbreviated interview or mailed questionnaire was completed by willing non-respondents, most of whom had refused participation in the main study.

RESULTS

Respondents and non-respondents appeared similar with respect to age, race, relative weight, smoking, family history of breast cancer, number of births, age at first birth, and several dietary items. Compared to non-respondents, case and control respondents were of shorter stature, and reported less frequent consumption of doughnuts/pastries. Respondent cases, compared with non-respondent cases, were more highly educated and more likely to have consumed alcohol regularly; similar but not statistically significant tendencies were observed for controls. Respondent cases experienced menarche earlier than non-respondents. Respondent controls were more likely to have used oral contraceptives than non-respondents; a similar but not statistically significant tendency was observed in cases. Comparisons of crude and simulated relative risks using available non-respondents' data generally showed a low impact of non-response on relative risks in this study.

CONCLUSIONS

Our results suggest that non-response would not greatly affect relative risk estimates in this study, except possibly regarding height. However, we were limited by the numbers of informative non-respondents and the amount of data collected. Collecting similar information in future studies would be useful, especially since varying methods used to encourage participation may lead to differences in respondents' characteristics.

Functional impairment, depression, and life satisfaction among older hemodialysis patients and age-matched controls: a prospective study

OBJECTIVE

To compare change over time in functional impairment, depression, and life satisfaction among older dialysis patients and age-matched controls.

DESIGN

Prospective cohort study over 3 years.

SETTING

Urban and rural communities throughout Georgia.

SUBJECTS

One hundred thirteen prevalent renal failure patients on in-center hemodialysis and 286 controls.

MAIN OUTCOME MEASURES

Ordinal functional impairment index and life satisfaction rating, and Center for Epidemiologic Studies Depression Scale.

RESULTS

Dialysis patients, compared with controls, reported significantly more functional impairment at baseline, and also at follow-up after adjusting for baseline impairment and covariates. Dialysis patients had higher depression scores at baseline, and also at follow-up after adjusting for baseline depression and covariates. In contrast, dialysis patients reported lower life satisfaction at baseline than did controls, but the two cohorts were not significantly different on reported life satisfaction at follow-up, after adjusting for baseline life satisfaction and race. In both cohorts, functional impairment and depression were significantly related.

CONCLUSION

Older dialysis patients' life satisfaction at a 3-year follow-up, which was similar to life satisfaction among age-matched controls, indicates the value of delivered dialysis care; the value of this care would be increased by reducing excess functional impairment in these patients.

Social and emotional competence in children of depressed mothers

The relation between maternal unipolar major depression and children's self-concept, self-control, and peer relationships were studied in a middle-class, predominantly white sample of 96 families. Each family included a target child between the ages of 5 and 10. Depressed mothers varied on whether or not the child's father also had a psychiatric disorder. Well mothers all had spouses with no psychiatric disorders. Analyses controlled for marital status, age, and sex of child. Children completed measures of self-concept and peer relations skills; teachers completed measures of self-control and a rating of popularity with peers. Results supported the multiple risk factor model in that fathers' psychiatric status and parents' marital status explained much of the variability in children's social and emotional competence. Maternal depression alone, in the context of a well husband/father, was only related to children having been rated by their teachers as less popular. Results are discussed in terms of possible mechanisms by which maternal depression may interact with paternal psychopathology and divorce in relation to children's social and emotional competence. The findings may further indicate that older children are more vulnerable to these multiple risk factors than younger children.

Menstrual risk factors and early-onset breast cancer

OBJECTIVES

Epidemiologic studies provide evidence for increased breast cancer risk among women with prolonged exposure to endogenous estrogens and progesterone. Menstrual cycle characteristics, such as early menarche, rapid initiation of regular ovulatory cycles, short cycle length, and more days of flow, all potentially contribute to higher cumulative ovarian hormone exposure.

METHODS

We assessed the associations between these characteristics and breast cancer risk in a population-based, case-control study of 1505 controls and 1647 newly diagnosed cases, all younger than 45 years of age.

RESULTS

Compared to women with menarche at > or =15 years, we observed some increase in risk for women with younger ages at menarche, although those with very early ages were not at particularly high risk [odds ratio (OR) = 1.5, 95% confidence interval (CI) = 1.1-1.9 for menarche at age 12 and OR = 1.2, 95% CI = 0.9-1.7 for menarche at age < or =10]. Women who reported having regular menstrual cycles within 2 years of menarche were at increased breast cancer risk (OR = 1.7, 95% CI = 1.2-2.3), compared to those never having regular cycles. Stratification by current body mass index revealed slightly stronger associations with menstrual characteristics among thinner women (< 22.0 kg/m2) compared to heavier women (> 28.8 kg/m2).

CONCLUSIONS

These findings suggest that future studies should focus on clarifying how the interrelated effects of body size and menstrual factors, such as age at menarche and cycle regularity, contribute to breast cancer etiology.

Race and restless sleep complaint in older chronic dialysis patients and nondialysis community controls

There is mixed evidence about the relation of race to risk of sleep disturbance. We explored the relation of race to restless sleep complaint in survey data from a cohort of 311 older patients undergoing chronic renal dialysis and a similarly aged cohort of 354 nondialysis controls. Older dialysis patients were significantly more likely to report restless sleep. Restless sleep complaint was related to comorbidity, depressed mood, use of sleep medications, and perceived health status in both groups. Black patients in the dialysis cohort had decreased odds of restless sleep, but Black and White controls did not differ significantly in reporting restless sleep. Compared with their more socially advantaged White counterparts, older Black dialysis patients may perceive the chronic dialysis care environment more favorably. The findings are consistent with the view that sleep quality in late life is likely to reflect a delicate balance between psychological as well as physical well-being.

Methodologic concerns in defining lesbian for health research

A recent report from the Institute of Medicine recommends more methodologic and substantive research on the health of lesbians. This study addresses one methodologic topic identified in the Institute of Medicine report and by a subsequent scientific workshop on lesbian health: the definition and assessment of sexual orientation among women. Data are from the Women Physicians' Health Study, a questionnaire-based U.S. probability sample survey (N = 4,501). The two items on sexual orientation (current self-identity and current sexual behavior) had a high response rate (96%), and cross-tabulation of responses indicated several combinations of identity and behavior. Three conceptually different definitions of "lesbian" are compared on the basis of (1) identity only, (2) sexual behavior only, and (3) both identity and sexual behavior. Suggestions and cautions are given to researchers who will add items on sexual orientation to new or ongoing research on women's health.

Epidemic poliomyelitis in The Gambia following the control of poliomyelitis as an endemic disease. II. Clinical efficacy of trivalent oral polio vaccine

An epidemic of poliomyelitis caused by poliovirus type 1 occurred in The Gambia from May to November 1986. Descriptive findings and vaccination coverage levels are reported in part I. This article (part II) describes a case-control study to estimate the clinical efficacy of three or more doses of trivalent oral polio vaccine compared with zero doses. "Cases" were 1- to 7-year-old children paralyzed during the epidemic who were diagnosed as having poliomyelitis by designated referral physicians. They were identified by reports from referral physicians during the epidemic and by a nationwide village-to-village search after the epidemic. Up to five controls were randomly selected for each case from among children of the same age and sex living in neighboring households. In a matched analysis of 195 cases and 839 controls, the efficacy of three or more doses of trivalent oral polio vaccine was 72% (95% confidence interval 57-82) when children without vaccination cards were considered unvaccinated. The efficacy of three or more doses in 1- to 2-year-old children, in whom the determination of vaccination status was considered to be more accurate than in older children, was 81% (95% confidence interval 66-90). Vaccine failure was not associated with short intervals between doses. Higher levels of vaccination coverage and efficacy than those achieved in The Gambia may be needed in African countries to prevent the return of poliomyelitis as an epidemic disease after it has been controlled as an endemic disease.