Switching to "lighter" cigarettes and quitting smoking

OBJECTIVE

Smokers who switch to "lighter" cigarettes may be diverted from quitting smoking. We assessed factors associated with switching and the association between switching and (1) making a quit attempt, and (2) recent quitting, yielding a measure of net quitting (attempts x recent quitting).

DESIGN

In 2003, a total of 30 800 ever-smokers who smoked in the past year provided history of switching and 3 reasons for switching: harm reduction, quitting smoking and flavour. Among those who made a past-year quit attempt, recent quitting was defined as >or=90-day abstinence when surveyed. Multivariable logistic regression identified determinants of outcomes.

RESULTS

In all, 12 009 (38%) of ever-smokers switched. Among switchers, the most commonly cited reasons were flavour only (26%) and all 3 reasons (18%). Switchers (vs non-switchers) were more likely to make a quit attempt between 2002 and 2003 (51% vs 41%, p<0.001, adjusted odds ratio (AOR) 1.58, (95% confidence interval (CI) 1.48 to 1.69)), but less likely to have recently quit (9% vs 17%, p<0.001; AOR 0.40 (95% CI 0.35 to 0.45)), yielding lower overall net quitting (4.3% vs 7.0%, p<0.001; AOR 0.54, (95% CI 0.47 to 0.61)). The effects of switching on outcomes were most pronounced for reasons including quitting smoking, whereas switching for harm reduction alone had no association with outcomes.

CONCLUSION

Compared with no switching, a history of switching was associated with 46% lower odds of net quitting.

State-specific trends in smoke-free workplace policy coverage: the current population survey tobacco use supplement, 1993 to 1999

We examined trends in smoke-free workplace policies among all indoor workers in the United States using the National Cancer Institute's Tobacco Use Supplement to the Census Bureau's Current Population Survey (total n = 270,063). Smoke-free was defined as smoking not permitted in public or common areas or in work areas of a worksite. Nationally, we found that nearly 70% of the US workforce worked under a smoke-free policy in 1999. At the state level, a greater than 30-percentage-point differential existed in the proportion of workers with such policies. Although significant progress has been made to reduce worker exposure to environmental tobacco smoke on the job, we predict further progress may be difficult unless comprehensive regulations to protect all workers are implemented at the national, state, or local level.

Sex differences in workplace smoking policies: results from the current population survey

OBJECTIVE

To determine the prevalence of smoking policies in indoor work environments in the United States, with a special focus on sex differences in the provision of these policies.

METHOD

Information on the prevalence and restrictiveness of workplace smoking policies was obtained from 86,490 currently employed indoor workers (50,865 women and 35,625 men) 15 years of age and older who responded to the National Cancer Institute's Tobacco Use Supplement to the Current Population Survey, a cross-sectional survey of households in all 50 states and the District of Columbia conducted between 1995 and 1996.

RESULTS

Eighty-six percent of respondents reported that their workplaces had official smoking policies, and 63% reported that their workplaces were smoke free. Women reported significantly higher rates of both official smoking policies and smoke-free workplaces than men, regardless of racial/ethnic or age group.

CONCLUSION

The overall rates of worksite smoking restrictions, including the establishment of smoke-free workplaces, were higher than those reported in earlier surveys. Disparities in coverage will need to be reduced if all workers, regardless of sex, race, age, or industry of employment, are to be protected from the demonstrated hazards of environmental tobacco smoke.

Effects of supplemental alpha-tocopherol and beta-carotene on urinary tract cancer: incidence and mortality in a controlled trial (Finland)

OBJECTIVES

Epidemiological studies have suggested a protective effect of vegetables and fruits on urinary tract cancer but the possible protective nutrients are unknown. We studied the effect of alpha-tocopherol (a form of vitamin E) and beta-carotene supplementation on urinary tract cancer in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study.

METHODS

A total of 29,133 male smokers aged 50-69 years from southwestern Finland were randomly assigned to receive alpha-tocopherol (50 mg), beta-carotene (20 mg), both agents, or a placebo daily for 5-8 years (median 6.1 years). Incident urothelial cancers (bladder, ureter, and renal pelvis; n = 169) and renal cell cancers (n = 102) were identified through the nationwide cancer registry. The diagnoses were centrally confirmed by review of medical records and pathology specimens. The supplementation effects were estimated using a proportional hazards model.

RESULTS

Neither alpha-tocopherol nor beta-carotene affected the incidence of urothelial cancer, relative risk 1.1 (95% confidence interval (CI) 0.8-1.5) and 1.0 (95% CI 0.7-1.3), respectively, or the incidence of renal cell cancer, relative risk 1.1 (95% CI 0.7-1.6) and 0.8 (95% CI 0.6-1.3), respectively.

CONCLUSION

Long-term supplementation with alpha-tocopherol and beta-carotene has no preventive effect on urinary tract cancers in middle-aged male smokers.

Index for US state tobacco control initial outcomes

Public health tobacco control efforts have increasingly targeted communities in addition to individuals. Before population smoking decreases, effectiveness might be detected from initial outcomes reflecting these efforts, such as higher cigarette prices or more workplace and home smoking restrictions. Presumably, these initial outcomes will eventually influence smoking behavior. State-specific estimates of percentages of the population working or living under smoking bans are available from the 1992-1993 tobacco use supplement to the Current Population Survey, conducted annually by the US Bureau of the Census. In addition, the tobacco industry reports the average state cigarette price yearly. The authors constructed a tobacco control initial outcomes index (IOI) by using values of these variables for each state and correlated it with state-specific adult (aged > or =25 years) and youth (aged 15-24 years) smoking prevalence computed from the Current Population Survey and per capita cigarette consumption data computed from sales and Census Bureau data. Both adult smoking prevalence (r = -0.70) and per capita consumption (r = -0.73) were significantly correlated with the IOI; youth smoking prevalence correlated less well (r = -0.34). Although the analysis is not definitive, deseasonalized 1983-1997 consumption trends for IOI-based tertile groups were divergent beginning in 1993, with the high IOI group showing the greatest decrease. A high relative IOI index may be predictive of future smoking decreases and should be considered when tobacco control efforts are evaluated.

Effects of supplemental alpha-tocopherol and beta-carotene on colorectal cancer: results from a controlled trial (Finland)

BACKGROUND

Some epidemiological investigations suggest that higher intake or biochemical status of vitamin E and beta-carotene might be associated with reduced risk of colorectal cancer.

METHODS

We tested the effects of alpha-tocopherol and beta-carotene supplementation on the incidence of colorectal cancer in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study, a double-blind, placebo-controlled trial among 29,133 50-69-year-old male cigarette smokers. Participants were randomly assigned to receive alpha-tocopherol (50 mg), beta-carotene (20 mg), both agents, or a placebo daily for 5-8 years. Incident colorectal cancers (n = 135) were identified through the nationwide cancer registry, and 99% were histologically confirmed. Intervention effects were evaluated using survival analysis and proportional hazards models.

RESULTS

Colorectal cancer incidence was somewhat lower in the alpha-tocopherol arm compared to the no alpha-tocopherol arm, but this finding was not statistically significant (relative risk (RR) = 0.78, 95% confidence interval (CI) 0.55-1.09; log-rank test p = 0.15). Beta-carotene had no effect on colorectal cancer incidence (RR = 1.05, 95% CI 0.75-1.47; log-rank test p = 0.78). There was no interaction between the two substances.

CONCLUSION

Our study found no evidence of a beneficial or harmful effect for beta-carotene in colorectal cancer in older male smokers, but does provide suggestive evidence that vitamin E supplementation may have had a modest preventive effect. The latter finding is in accord with previous research linking higher vitamin E status to reduced colorectal cancer risk.

Effects of supplemental alpha-tocopherol and beta-carotene on colorectal cancer: results from a controlled trial (Finland)

BACKGROUND

Some epidemiological investigations suggest that higher intake or biochemical status of vitamin E and beta-carotene might be associated with reduced risk of colorectal cancer.

METHODS

We tested the effects of alpha-tocopherol and beta-carotene supplementation on the incidence of colorectal cancer in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study, a double-blind, placebo-controlled trial among 29,133 50-69-year-old male cigarette smokers. Participants were randomly assigned to receive alpha-tocopherol (50 mg), beta-carotene (20 mg), both agents, or a placebo daily for 5-8 years. Incident colorectal cancers (n = 135) were identified through the nationwide cancer registry, and 99% were histologically confirmed. Intervention effects were evaluated using survival analysis and proportional hazards models.

RESULTS

Colorectal cancer incidence was somewhat lower in the alpha-tocopherol arm compared to the no alpha-tocopherol arm, but this finding was not statistically significant (relative risk (RR) = 0.78, 95% confidence interval (CI) 0.55-1.09; log-rank test p = 0.15). Beta-carotene had no effect on colorectal cancer incidence (RR = 1.05, 95% CI 0.75-1.47; log-rank test p = 0.78). There was no interaction between the two substances.

CONCLUSION

Our study found no evidence of a beneficial or harmful effect for beta-carotene in colorectal cancer in older male smokers, but does provide suggestive evidence that vitamin E supplementation may have had a modest preventive effect. The latter finding is in accord with previous research linking higher vitamin E status to reduced colorectal cancer risk.

A comparison of prospective and retrospective assessments of diet in a study of colorectal cancer

Dietary factors are widely studied as risk factors for colorectal cancer, with much information from case-control studies. We evaluated the validity of dietary data from a retrospective case-control study of diet and colorectal cancer. As part of the alpha-Tocopherol, beta-Carotene Cancer Prevention Study, diet was assessed at baseline and after diagnosis for colorectal cancer cases and at baseline and regularly during the trial for a random control group. The dietary assessment referred to the previous 12 months (in cases before diagnosis). In the two dietary assessments, the cases reported a greater increase in consumption of fruits and dairy products and a decrease in consumption of potatoes. Accordingly, relative risks for colorectal cancer by baseline dietary data differed markedly from odds ratios from case-control data; e.g., relative risk for a 652-mg increase in calcium intake was 0.79 (95% confidence interval = 0.48-1.30) in case-cohort analysis vs. an odds ratio of 1.57 (95% confidence interval = 1.06-2.33) for case-control analysis. The most likely explanation is the influence of current diet on recall of prediagnosis diet and effects of occult cancer on diet in the year before cancer diagnosis, which have implications for interpretation of case-control studies in evaluating associations between diet and colorectal cancer.

Incidence of cataract operations in Finnish male smokers unaffected by alpha tocopherol or beta carotene supplements

OBJECTIVE

To examine the effect of alpha tocopherol and beta carotene supplementation on the incidence of age related cataract extraction.

SETTING

The Alpha-tocopherol Beta-carotene (ATBC) Study was a randomised, double blind, placebo controlled, 2 x 2 factorial trial conducted in south western Finland. The cataract surgery study population of 28,934 male smokers 50-69 years of age at the start.

INTERVENTION

Random assignment to one of four regimens: alpha tocopherol 50 mg per day, beta carotene 20 mg per day, both alpha tocopherol and beta carotene, or placebo. Follow up continued for five to eight years (median 5.7 years) with a total of 159,199 person years.

OUTCOME MEASURE

Cataract extraction, ascertained from the National Hospital Discharge Registry.

RESULTS

425 men had cataract surgery because of senile or presenile cataract during the follow up. Of these, 112 men were in the alpha tocopherol alone group, 112 men in the beta carotene alone group, 96 men in the alpha tocopherol and beta carotene group, and 105 men in the placebo group. When supplementation with alpha tocopherol and with beta carotene were introduced to a Cox proportional hazards model with baseline characteristics (age, education, history of diabetes, body mass index, alcohol consumption, number of cigarettes smoked daily, smoking duration, visual acuity, and total cholesterol), neither alpha tocopherol (relative risk, RR, 0.91, 95% confidence intervals, CI, 0.74, 1.11) nor beta carotene (RR 0.97, 95% CI 0.79, 1.19) supplementation affected the incidence of cataract surgery.

CONCLUSION

Supplementation with alpha tocopherol or beta carotene does not affect the incidence of cataract extractions among male smokers.

The association between baseline vitamin E, selenium, and prostate cancer in the alpha-tocopherol, beta-carotene cancer prevention study

The association between prostate cancer and baseline vitamin E and selenium was evaluated in the trial-based cohort of the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study (n = 29,133). During up to 9 years of follow-up, 317 men developed incident prostate cancer. Multivariate Cox proportional hazards models that adjusted for intervention group, benign prostatic hyperplasia, age, smoking, and urban residence were used to evaluate associations between prostate cancer and exposures of interest. There were no significant associations between baseline serum alpha-tocopherol, dietary vitamin E, or selenium and prostate cancer overall. The associations between prostate cancer and vitamin E and some of the baseline dietary tocopherols differed significantly by alpha-tocopherol intervention status, with the suggestion of a protective effect for total vitamin E among those who received the alpha-tocopherol intervention (relative risk was 1.00, 0.68, 0.80, and 0.52 for increasing quartiles; P = 0.07).

Prostate cancer and supplementation with alpha-tocopherol and beta-carotene: incidence and mortality in a controlled trial

BACKGROUND

Epidemiologic studies have suggested that vitamin E and beta-carotene may each influence the development of prostate cancer. In the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study, a controlled trial, we studied the effect of alpha-tocopherol (a form of vitamin E) and beta-carotene supplementation, separately or together, on prostate cancer in male smokers.

METHODS

A total of 29133 male smokers aged 50-69 years from southwestern Finland were randomly assigned to receive alpha-tocopherol (50 mg), beta-carotene (20 mg), both agents, or placebo daily for 5-8 years (median, 6.1 years). The supplementation effects were estimated by a proportional hazards model, and two-sided P values were calculated.

RESULTS

We found 246 new cases of and 62 deaths from prostate cancer during the follow-up period. A 32% decrease (95% confidence interval [CI] = -47% to -12%) in the incidence of prostate cancer was observed among the subjects receiving alpha-tocopherol (n = 14564) compared with those not receiving it (n = 14569). The reduction was evident in clinical prostate cancer but not in latent cancer. Mortality from prostate cancer was 41% lower (95% CI = -65% to -1%) among men receiving alpha-tocopherol. Among subjects receiving beta-carotene (n = 14560), prostate cancer incidence was 23% higher (95% CI = -4%-59%) and mortality was 15% higher (95% CI = -30%-89%) compared with those not receiving it (n = 14573). Neither agent had any effect on the time interval between diagnosis and death.

CONCLUSIONS

Long-term supplementation with alpha-tocopherol substantially reduced prostate cancer incidence and mortality in male smokers. Other controlled trials are required to confirm the findings.

Effect of measurement error on energy-adjustment models in nutritional epidemiology

The use and interpretation of energy-adjustment regression models in nutritional epidemiology has been vigorously debated recently. There has been little discussion, however, regarding the effect of dietary measurement error on the performance of such models. Contrary to conventional assumptions invoked in the standard treatment of the effect of measurement error in regression analysis, reporting errors in dietary studies are usually biased, correlated with true nutrient intakes and with each other, heteroscedastic, and nonnormally distributed. Methods developed in this paper allow for this more complex error structure and are therefore more appropriate for dietary data. For practical illustration, these methods are applied to data from the Women's Health Trial Vanguard Study. The results demonstrate considerable shrinkage in the magnitude of the estimated main exposure effect in energy-adjustment models due to attenuation of the true effect and contamination from the effect of an adjusting covariate. In most cases, this shrinkage causes a sharply reduced statistical power of the corresponding significance test in comparison with measurement without error. These results emphasize the need to understand the measurement error properties of dietary instruments through validation/calibration studies and, where possible, to correct for the impact of measurement error when applying energy-adjustment models.

Workplace smoking policies in the United States: results from a national survey of more than 100,000 workers

OBJECTIVE

To determine the prevalence of smoking policies in indoor work environments as reported by a nationally representative sample of workers in the United States.

DESIGN

Cross-sectional survey of households within the United States.

SETTING

All 50 state and the District of Columbia, 1992-93.

PARTICIPANTS

Currently employed indoor workers 15 years of age and older who responded to the National Cancer Institute's Tobacco Use Supplement to the Current Population Survey (n = 100,561).

MAIN OUTCOME MEASURES

The prevalence and restrictiveness of workplace smoking policies as reported by workers currently employed in indoor workplaces in the United States.

RESULTS

Most of the indoor workers surveyed (81.6%) reported that their place of work had an official policy that addressed smoking in the workplace; 46.0% reported that their workplace policy did not permit smoking in either the public/common areas--for example, restrooms and cafeterias--or the work areas of the workplace. The reporting of these "smoke-free" policies varied significantly by gender, age, race/ethnicity, smoking status, and occupation of the worker.

CONCLUSIONS

Although nearly half of all indoor workers in this survey reported that they had a smoke-free policy in their workplace, significant numbers of workers, especially those in blue-collar and service occupations, reported smoke-free rates well below the national average. If implemented, the US Occupational Safety and Health Administration's proposed regulation to require worksites to be smoke-free has the potential to increase significantly the percentage of American workers covered by these policies and to eliminate most of the disparity currently found across occupational groups.

Intake of fatty acids and risk of coronary heart disease in a cohort of Finnish men. The Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study

The relation of intakes of specific fatty acids and the risk of coronary heart disease was examined in a cohort of 21,930 smoking men aged 50-69 years who were initially free of diagnosed cardiovascular disease. All men participated in the Finnish Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study and completed a detailed and validated dietary questionnaire at baseline. After 6.1 years of follow-up from 1985-1988, the authors documented 1,399 major coronary events and 635 coronary deaths. After controlling for age, supplement group, several coronary risk factors, total energy, and fiber intake, the authors observed a significant positive association between the intake of trans-fatty acids and the risk of coronary death. For men in the top quintile of trans-fatty acid intake (median = 6.2 g/day), the multivariate relative risk of coronary death was 1.39 (95% confidence interval (CI) 1.09-1.78) (p for trend = 0.004) as compared with men in the lowest quintile of intake (median = 1.3 g/day). The intake of omega-3 fatty acids from fish was also directly related to the risk of coronary death in the multivariate model adjusting also for trans-saturated and cis-monounsaturated fatty acids (relative risk (RR) = 1.30, 95% CI 1.01-1.67) (p for trend = 0.06 for men in the highest quintile of intake compared with the lowest). There was no association between intakes of saturated or cis-monounsaturated fatty acids, linoleic or linolenic acid, or dietary cholesterol and the risk of coronary deaths. All the associations were similar but somewhat weaker for all major coronary events.

Validity of diagnoses of major coronary events in national registers of hospital diagnoses and deaths in Finland

We validated diagnoses of acute myocardial infarction (AMI) and death from coronary heart disease (CHD) found in the Finnish National Hospital Discharge Register and the Register of Causes of Death from a sample of the 29,133 men participating in the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study. The cases were traced to hospitals and institutes performing medico-legal death cause examinations and all relevant information was collected. The cardiac events were re-evaluated according to the diagnostic criteria of the Finnish contribution to the WHO MONICA project, i.e. the FINMONICA criteria. Altogether 408 cases of non-fatal AMI (n = 217) and death from CHD (n = 191) were reviewed. In the re-evaluation 94% of them (95% confidence interval 92-96%) were diagnosed as either definite (57%) or possible (37%) AMI. Non-fatal cases were more often classified definite AMI in the review, whereas fatal cases were more often classified possible AMI. Age or trial supplementation group did not affect classification, and no secular trend was observed. In conclusion, the diagnoses of AMI and death from CHD in the registers were highly predictive of a true major coronary event defined by strict criteria, thus their use in endpoint assessment in epidemiological studies and clinical trials is justified.

Cigarette smoking among U.S. adults by state and region: estimates from the current population survey

BACKGROUND

Cigarette smoking is responsible for at least one third of all cancer deaths annually in the United States. Few sources exist in the peer-reviewed literature documenting state and regional differences in smoking behavior, despite the fact that cancer prevention and control efforts are increasingly being implemented below the national level.

PURPOSE

Our goals were to determine smoking prevalence rates among men and women, by region, and for each of the 50 states and the District of Columbia from census survey data collected in 1992 and 1993 and to compare these rates with rates determined in 1985.

METHODS

Every month, the U.S. Bureau of the Census collects labor force statistics on more than 100000 individuals on its Current Population Survey (CPS). For the September 1992, January 1993, and May 1993 CPS, the National Cancer Institute sponsored a 40-item Tobacco Use Supplement. The definition of a current smoker changed slightly between 1985 and 1992-1993. For the 1985 CPS, individuals were considered current smokers if they had smoked 100 cigarettes in their lifetime and were smoking at the time of interview; for the 1992-1993 CPS, current smokers included anyone who had smoked 100 cigarettes and was currently smoking every day or just on some days. We calculated current smoking rates (every day and some days combined) based on more than a quarter million adults (n = 266988) interviewed in 1992-1993.

RESULTS

Substantial geographic variation exists in rates of current cigarette use among adults within the United States. In general, adults in the southern United States have higher rates of smoking and adults in the western states have lower rates of smoking and adults in the rest of the country, although differences in smoking behavior between men and women and among various racial and ethnic populations strongly influence these patterns. Only two states, Kentucky and West Virginia, exhibited adult smoking rates (men and women combined) of 30% or higher in 1992-1993; in contrast, in 1985, such rates were reported from 20 states. The only states in which the prevalence was below 20% in 1992-1993 were Utah (17.1%) and California (19.5%). Rates approaching 20% were reported from New Jersey (20.7%), Massachusetts (21.5%), and Nebraska, New York, and Hawaii (22.0% each) in 1992-1993. Rhode Island experienced the greatest relative decline in smoking prevalence from 1985 to 1992-1993, with a calculated relative change of -30.7% (based on a change in rate from 33.5% to 23.2%), followed by Delaware (-25.9%) the District of Columbia and New Jersey (-23.9% each), Connecticut (-23.2%), California (-22.9%), Alaska (-22.8%), Georgia (-22.6%), Massachusetts (-22.1%), and New York (-22.0%).

CONCLUSIONS

Smoking rates are not uniform in the United States but vary considerably from state to state, even within the same region of the country. The CPS is the only mechanism currently capable of simultaneously monitoring smoking trends nationally, regionally, and on a state-by-state basis.

Intake of dietary fiber and risk of coronary heart disease in a cohort of Finnish men. The Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study

BACKGROUND

Even though dietary fiber has been hypothesized to reduce the risk of coronary heart disease, few large epidemiological studies have examined this relation with good methodology.

METHODS AND RESULTS

The Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study was a randomized, double-blind, placebo-controlled trial with daily supplementation of alpha-tocopherol and/or beta-carotene. Of the participants, 21930 smoking men aged 50 to 69 years who were free of diagnosed cardiovascular disease and had completed a validated dietary questionnaire at baseline were followed for 6.1 years. We monitored the incidence of major coronary events (a combination of first nonfatal myocardial infarction and coronary heart disease death; n = 1399) and mortality from coronary heart disease (n = 635). Both entities had a significant inverse association with dietary fiber, but the association was stronger for coronary death. For men in the highest quintile of total dietary fiber intake (median, 34.8 g/d), the relative risk for coronary death was 0.69 (95% confidence interval, 0.54 to 0.88; P < .001 for trend) compared with men in the lowest quintile of intake (median, 16.1 g/d). With an adjustment for known cardiovascular risk factors, intake of saturated fatty acids, beta-carotene, vitamin C, and vitamin E did not materially change the result. Water-soluble fiber was slightly more strongly associated with reduced coronary death than water-insoluble fiber, and cereal fiber also had a stronger association than vegetable or fruit fiber.

CONCLUSIONS

These findings suggest that independent of other risk factors, greater intake of foods rich in fiber can substantially reduce the risk of coronary heart disease, and particularly coronary death, in middle-aged, smoking men.

Alpha-Tocopherol and beta-carotene supplements and lung cancer incidence in the alpha-tocopherol, beta-carotene cancer prevention study: effects of base-line characteristics and study compliance

BACKGROUND

Experimental and epidemiologic investigations suggest that alpha-tocopherol (the most prevalent chemical form of vitamin E found in vegetable oils, seeds, grains, nuts, and other foods) and beta-carotene (a plant pigment and major precursor of vitamin A found in many yellow, orange, and dark-green, leafy vegetables and some fruit) might reduce the risk of cancer, particularly lung cancer. The initial findings of the Alpha-Tocopherol, Beta-Carotene Cancer Prevention Study (ATBC Study) indicated, however, that lung cancer incidence was increased among participants who received beta-carotene as a supplement. Similar results were recently reported by the Beta-Carotene and Retinol Efficacy Trial (CARET), which tested a combination of beta-carotene and vitamin A.

PURPOSE

We examined the effects of alpha-tocopherol and beta-carotene supplementation on the incidence of lung cancer across subgroups of participants in the ATBC Study defined by base-line characteristics (e.g., age, number of cigarettes smoked, dietary or serum vitamin status, and alcohol consumption), by study compliance, and in relation to clinical factors, such as disease stage and histologic type. Our primary purpose was to determine whether the pattern of intervention effects across subgroups could facilitate further interpretation of the main ATBC Study results and shed light on potential mechanisms of action and relevance to other populations.

METHODS

A total of 29,133 men aged 50-69 years who smoked five or more cigarettes daily were randomly assigned to receive alpha-tocopherol (50 mg), beta-carotene (20 mg), alpha-tocopherol and beta-carotene, or a placebo daily for 5-8 years (median, 6.1 years). Data regarding smoking and other risk factors for lung cancer and dietary factors were obtained at study entry, along with measurements of serum levels of alpha-tocopherol and beta-carotene. Incident cases of lung cancer (n = 894) were identified through the Finnish Cancer Registry and death certificates. Each lung cancer diagnosis was independently confirmed, and histology or cytology was available for 94% of the cases. Intervention effects were evaluated by use of survival analysis and proportional hazards models. All P values were derived from two-sided statistical tests.

RESULTS

No overall effect was observed for lung cancer from alpha-tocopherol supplementation (relative risk [RR] = 0.99; 95% confidence interval [CI] = 0.87-1.13; P = .86, logrank test). beta-Carotene supplementation was associated with increased lung cancer risk (RR = 1.16; 95% CI = 1.02-1.33; P = .02, logrank test). The beta-carotene effect appeared stronger, but not substantially different, in participants who smoked at least 20 cigarettes daily (RR = 1.25; 95% CI = 1.07-1.46) compared with those who smoked five to 19 cigarettes daily (RR = 0.97; 95% CI = 0.76-1.23) and in those with a higher alcohol intake (> or = 11 g of ethanol/day [just under one drink per day]; RR = 1.35; 95% CI = 1.01-1.81) compared with those with a lower intake (RR = 1.03; 95% CI = 0.85-1.24).

CONCLUSIONS

Supplementation with alpha-tocopherol or beta-carotene does not prevent lung cancer in older men who smoke. beta-Carotene supplementation at pharmacologic levels may modestly increase lung cancer incidence in cigarette smokers, and this effect may be associated with heavier smoking and higher alcohol intake.

IMPLICATIONS

While the most direct way to reduce lung cancer risk is not to smoke tobacco, smokers should avoid high-dose beta-carotene supplementation.

Use of semiquantitative food frequency questionnaires to estimate the distribution of usual intake

The authors consider whether semiquantitative food frequency questionnaires can be used to survey a population to estimate the distribution of usual intake. They take as an assumption that, if they were possible to obtain, the mean of many food records or recalls would be an accurate representation of an individual's usual diet. They then assume that nutrient intake as measured by a questionnaire follows a linear regression model when regressed against the usual intake of that nutrient. If the coefficients in this regression relation were known, then the distribution of usual intake could be constructed from the responses to the questionnaire. Since one generally does not know the values of the coefficients, they need to be estimated from a calibration study in which respondents complete the questionnaire together with multiple food records or recalls. This can be done either through an internal subset of the data or through an independent external study. With an internal substudy, the authors find that food frequency questionnaires typically provide little information about the distribution of usual intake in addition to that obtained from the multiple records or recalls in the substudy. When the substudy is external, if it is small then having very large numbers of subjects completing food frequency questionnaires in the survey is no more efficient than having a few subjects completing food records or recalls. However, if the external substudy is large and accurately characterizes the relation between the questionnaire response and usual intake, food frequency questionnaires can provide a cost-efficient way of estimating the distribution of usual intake. These results do not apply to the different problem of correcting relative risks for the effects of measurement error.

Reproducibility of a self-administered diet history questionnaire administered three times over three different seasons

The reproducibility of the widely used Health Habits and History Questionnaire (HHHQ) for estimating "usual past-year" nutrient intake was examined. The HHHQ was self-administered on three occasions during three different seasons; 68 women (avg age 43 yrs) provided usable data for all three questionnaires in the appropriate seasons. Intraclass correlations (ICC) among the three administrations ranged from 0.56 (carotene) to 0.82 (fat as percentage of energy), with a median of 0.72. Thus, reliability was moderate to good, and season of administration/ordinality generally had little impact on ranking of individuals. The point estimates of intake of energy and a number of nutrients were higher in the first administration (winter). Except for dietary fiber and possibly carotene, most differences disappeared when adjusted for energy using a nutrient density approach, as well as using repeated-measures regression models. The higher intake in the first administration may be due more to either learning or fatigue effect rather than an effect of seasonal food availability on perceptions of "usual" intake. These data should be used in conjunction with validity data in the future to help evaluate the gain in precision of group means (and changes in these means) and improved estimates of odds ratios and correlations between nutrients and factors such as serum values, if a questionnaire is administered more than once.

Effects of alpha-tocopherol and beta-carotene supplements on cancer incidence in the Alpha-Tocopherol Beta-Carotene Cancer Prevention Study

The Alpha-Tocopherol Beta-Carotene (ATBC) Cancer Prevention Study was a placebo-controlled, randomized intervention trial testing the hypothesis that beta-carotene and alpha-tocopherol (vitamin E) supplements prevent lung and other cancers. The study is predicated on a substantial body of evidence supporting a role in cancer prevention for these micronutrients. Based on the 2 x 2 factorial study design, 29,133 eligible male cigarette smokers aged 50-69 y were randomly assigned to receive beta-carotene (20 mg), alpha-tocopherol (50 mg), beta-carotene and alpha-tocopherol, or placebo daily for 5-8 y. Capsule compliance was high (median = 99%). beta-Carotene treatment did not result in a decrease in cancer at any of the major sites but rather in an increase at several sites, most notably lung, prostate, and stomach (number of cases 474 compared with 402, 138 compared with 112, and 70 compared with 56, respectively). The vitamin E group had fewer incident cancers of the prostate and colorectum compared with the group not receiving vitamin E (number of cases 99 compared with 151 and 68 compared with 81, respectively), but more cancers of the stomach (70 compared with 56). In contrast to these intervention-based findings for beta-carotene and vitamin E supplements, we observed lower lung cancer rates in men with higher amounts of both serum and dietary beta-carotene and vitamin E at baseline.

Smoking behavior, workplace policies, and public opinion regarding smoking restrictions in Maryland

The Maryland Occupational Safety and Health (MOSH) advisory board recently proposed a smoking ban in most Maryland workplaces, including bars and restaurants, unless smoking is restricted to a separately ventilated area where nonsmoking workers cannot be required to enter. Results from the 1992-1993 Current Population Survey strongly suggest that there is broad support among Maryland residents for such restrictions and that the MOSH rules would merely extend an already widespread practice in the state. Efforts by the tobacco industry to gain an injunction against the proposed MOSH regulations would not appear to be supported by a clear majority of Maryland residents.

Revision of dietary analysis software for the Health Habits and History Questionnaire

The software for analysis of the Health Habits and History Questionnaire (HHHQ) has been revised and is available to researchers. As in earlier versions of the software, questionnaires other than the standard National Cancer Institute versions can be analyzed. Foods can be added or dropped, nutrients can be added or changed, and many other revisions and options are facilitated. Estimates of 33 nutrients and up to 20 user-defined food groups are produced. The validity is unchanged from the previous software. Other features include a data entry key-and-verify system, standardized editing, a computer-assisted interview, and the calculation of health indices including pack-years of smoking and social network index.

Contributions to the history of psychology: XCIX. Experimental study of infrahuman primate sexual behaviors: James Harlan Elder

Prior to the 1930s, designs of research into sexual behavior of infrahuman primates were not comparable; conclusions about physiological and nonphysiological factors in receptivity and mating were confounded by species studied, living and testing conditions, and precaptivity history. Clearly there was need for comprehensive and controlled studies of infrahuman primate sexual behavior. In response to the controversy about biological bases of receptivity and mating, James Harlan Elder, in collaboration with Robert M. Yerkes, designed the first truly comprehensive study of factors influencing sexual behavior of chimpanzees. At that time, other persons interested in this problem were employing experimental methods, but Elder's and Yerkes' program most directly addressed the problems confounding prior study and their work served as a model of experimental research into factors affecting receptivity and mating of infrahuman primates.

Energy adjustment methods for nutritional epidemiology: the effect of categorization

The authors discuss the interpretation of four alternative energy adjustment methods (Residual, Standard, Partition, and Nutrient Density) that have been proposed for the analysis of nutritional epidemiology studies. These methods have so far been compared under circumstances where intake of the nutrient of interest is measured as a continuous variable. Because it is common practice to categorize nutrient intakes in the analysis, the authors investigate the effect of such categorization on the interpretation of results from the four methods with the use of computer simulations and statistical theory. They consider four cases: where the nutrient intake is either divided into quartiles or ordered so as to investigate trend over the quartile groups, combined with using an adjusting variable that is either continuous or categorized. The results show: 1) the Residual, Standard, and Partition methods are no longer equivalent as they are in the continuous case; 2) compared with the Standard method, the Residual method appears to be more powerful for detecting trends in relative odds, is more robust to residual confounding when the adjustment variable is categorized, and provides more meaningful odds ratios; and 3) the Residual and Nutrient Density methods give closely similar results.

Clinical and laboratory adverse effects associated with long-term, low-dose isotretinoin: incidence and risk factors. The Isotretinoin-Basal Cell Carcinomas Study Group

Adverse effects associated with the long-term low-dose regimens of retinoids used in cancer chemoprevention studies are not well described. In order to examine the clinical and laboratory adverse effects of 3 years of intervention with isotretinoin (10 mg/day) and to assess potential risk factors for developing these, we collected adverse effect data on patients participating in a randomized, placebo-controlled trial designed to evaluate the effectiveness of isotretinoin in preventing the subsequent occurrence of new basal cell carcinoma. Our results showed a significantly higher incidence of adverse mucocutaneous effects and serum triglyceride elevations in the isotretinoin group (P < 0.001). Associated risk factors included male gender, very fair skin, and elevated pretreatment triglyceride levels. The toxicity observed, although less severe and less frequent, was similar to that seen with higher doses and should be weighed with adverse skeletal effects when considering long-term treatment of patients with moderate cancer risk.

Skeletal hyperostosis in patients receiving chronic, very-low-dose isotretinoin

BACKGROUND AND DESIGN

We conducted a prospective roentgenographic survey of patients participating in a randomized, placebo-controlled, multicenter clinical trial that evaluated the effectiveness of chronic, very-low-dose (approximately 0.14 mg/kg per day for 3 years) isotretinoin in preventing the subsequent occurrences of new basal cell carcinoma in patients with previous basal cell carcinoma. To assess potential skeletal changes, a sample of 269 patients from among a total of 981 enrollees were randomly selected for comparative roentgenographic review. Baseline and 36-month roentgenograms of the cervical and thoracic spine of each patient were read side by side by a radiologist, masked to treatment group, who noted both the presence and extent of abnormalities at each vertebral level at baseline and the progression of existing or occurrence of new abnormalities at previously unaffected levels at 36 months.

RESULTS

In comparison with the placebo group, significantly more patients in the isotretinoin group exhibited progression of existing hyperostotic abnormalities (40% vs 18%; P less than .001) and new hyperostotic involvement at previously unaffected vertebral levels (8% vs 1%; P = .015).

CONCLUSION

Our findings indicate that chronic, very-low-dose isotretinoin can induce hyperostotic axial skeletal changes similar to those reported in patients taking higher doses.

Comparison of two dietary questionnaires validated against multiple dietary records collected during a 1-year period

The validity of two dietary history questionnaires was examined, one the Health Habits and History Questionnaire (HHHQ) developed by Block et al and the other a questionnaire developed by investigators at the University of Michigan (UM). The reference data consisted of the mean of four 4-day dietary records and recalls collected for 1 year before administration of the questionnaires. The sample of 85 persons included black and white men and women aged 25 to 50 years. The HHHQ was entirely self-administered; the UM questionnaire had both self- and interviewer-administered components. The HHHQ group means were similar to food record estimates for energy and most nutrients, whereas the UM questionnaire produced overestimates for energy and all nutrients examined. Correlations ranged from .31 to .60 (median = .48) for the UM questionnaire and from .42 to .68 (median = .57) for the HHHQ. Use of respondent-reported portion sizes with the HHHQ produced higher correlations than use of investigator-determined "standard" portion sizes (median r = .43 vs .57). Food frequency questionnaires can provide useful nutrient data for individuals as well as groups.

Long-term therapy with low-dose isotretinoin for prevention of basal cell carcinoma: a multicenter clinical trial. Isotretinoin-Basal Cell Carcinoma Study Group

BACKGROUND

High-dose isotretinoin has been reported to have a prophylactic effect on nonmelanoma skin cancer, although it is associated with significant toxicity.

PURPOSE

To test the effectiveness of the long-term administration of low-dose isotretinoin in reducing the occurrence of basal cell carcinoma at a new site in patients with previously treated basal cell carcinomas and to measure the toxicity associated with this regimen, we conducted a clinical trial at eight cancer centers.

METHODS

Nine hundred and eighty-one patients with two or more previously confirmed basal cell carcinomas were randomly assigned to receive either 10 mg of isotretinoin or a placebo daily. Patients were followed for 36 months and monitored at 6-month intervals for skin cancer and toxic effects.

RESULTS

After 36 months of treatment, no statistically significant difference in either the cumulative percent of patients with an occurrence of basal cell carcinoma at a new site or the annual rate of basal cell carcinoma formation existed between patients receiving isotretinoin and those receiving the placebo. Elevated serum triglycerides, hyperostotic axial skeletal changes, and mucocutaneous reactions were more frequent in the group receiving isotretinoin than in the control group, and these differences were all statistically significant (P less than .001).

CONCLUSION

This low-dose regimen of isotretinoin not only is ineffective in reducing the occurrence of basal cell carcinoma at new sites in patients with two or more previously treated basal cell carcinomas but also is associated with significant adverse systemic effects.

IMPLICATION

The toxicity associated with the long-term administration of isotretinoin, even at the low dose used in this trial, must be weighted in planning future prevention trials.

Calibration of "pokes": psychophysical measurement of computer-generated temporal intervals

To answer questions raised about the accuracy of temporal intervals used to produce perception of apparent motion, interstimulus intervals generated by a computer were measured using physical and psychophysical procedures. Calibration of such devices was assumed initially to be routine but search of the literature indicated that calibration has been ignored in studies of motion and masking. Direct/physical methods of calibration proved unfeasible for assessing the accuracy of a computer programmed through "poke" procedures because signals for temporal intervals could not be differentiated from the output controlled by the machine's "hardwired" program. The results of psychophysical measurement of temporal intervals indicated that, on the average, differences, "constant errors" between expected/programmed intervals and matches of those intervals generally were less than six milliseconds.

Variability in nutrient and food intakes among older middle-aged men. Implications for design of epidemiologic and validation studies using food recording

The authors conducted a dietary methodology study in 1984 in Finnish men aged 55-69 years in order to validate two dietary assessment instruments being used in the US-Finland Alpha-Tocopherol, Beta-Carotene Lung Cancer Prevention Trial. Twelve 2-day food records collected from 162 men over a 6-month period, including every day of the week, served as the reference measure. This report focuses on three important questions for investigating diet and disease relations: 1) How many days are necessary to classify "usual" intake? 2) Is there loss as a result of using consecutive days? 3) Which days are necessary for assessment and classification of "usual" diet? A repeated-measures regression model was used to estimate the variance components and the effects of consecutive days, weekday (weekday vs. weekend), and season. Correlations between the averages of different numbers of days of food records and "true" usual intake were examined along with the resulting attenuations in relative risk. Results suggest that 7-14 days are required to adequately classify most individuals into categories of intake for most nutrients and some foods. There appears to be some loss of information from using consecutive days rather than days further apart. Weekday/weekend differences in mean intakes are slight, and the rank ordering of individuals appears to be preserved. A moderate seasonal effect is shown for classification of fruits, but only a slight one is seen for micronutrients and berries. Implications for the design of epidemiologic and validation studies are discussed.

The apparent validity of diet questionnaires is influenced by number of diet-record days used for comparison

The effect of the number of diet records used as the reference data on the apparent validity of a diet history questionnaire was examined using data from 97 participants in the Women's Health Trial feasibility study. Pearson correlation coefficients were computed between the estimates of usual individual intake from the questionnaire and estimates from the mean of three 4-day records obtained over a 1-year period, the mean of the two most recent records, and the record obtained 1 year after the start of the study. The results illustrate that the apparent validity of a questionnaire increases when it is compared with a greater number of 4-day food records. The correlations increased for most nutrients when the baseline food record was included, despite the fact that it was completed at a time not targeted by the questionnaire. These findings suggest that greater effort should be given to obtaining more diet-record days when validating other dietary assessment instruments.

A reduced dietary questionnaire: development and validation

A reduced questionnaire was developed by successively omitting segments of the full (98-item) Block questionnaire and calculating the correlations between nutrient estimates produced by the full and reduced versions. The reduced version contains 60 food items and requires 17 minutes to administer by an interviewer. It is intended to capture all nutrients in the diet, as is the full version. The reduced version was validated against three four-day records in a group of middle-aged women, and against two seven-day records collected 10-15 years ago in a group of older men. The absolute value of macronutrients estimated by the reduced questionnaire was lower than food-record estimates, but most micronutrients were not underestimated. For macronutrients correlations with food records were slightly lower with the reduced questionnaire, but for micronutrients there was only slight or no reduction in correlations as a result of using the reduced version. The brief version may be useful in studies that cannot allow the 30-35 minutes required for the full-length questionnaire.

Issues in reproducibility and validity of dietary studies

Numerous factors affect the reproducibility and validity of dietary assessment questionnaires. Although the respondents' abilities to respond accurately are most frequently discussed as the cause of apparently poor reproducibility and validity, many other factors are as important and perhaps more important. Most of these other factors are under the control of the investigator, and thus are amenable to improvement. Factors which may affect reproducibility included the degree of variability permitted by the instrument, the error-proneness of the response format, quality control of coding and keying and real dietary change in the time between the two administrations of the questionnaire. Factors affecting real or apparent validity include respondent characteristics, questionnaire design and quantification, quality control, and the adequacy of the reference data. The implications of inadequate reference data are illustrated and discussed.

Reproducibility and validity of dietary assessment instruments. II. A qualitative food frequency questionnaire

The reproducibility and validity of a food frequency questionnaire designed to measure intakes of total fat, saturated and polyunsaturated fats, vitamins A, C, and E, selenium, and dietary fiber were tested from March to October 1984 among 297 Finnish men aged 55-69 years. The questionnaire asked about consumption of 44 food items. In the reproducibility study, 107 subjects filled in the questionnaire three times, at three-month intervals. Intraclass correlations varied from 0.52 for vitamin A to 0.85 for polyunsaturated fat. In the validity study, 190 subjects kept food consumption records for 12 two-day periods distributed evenly over a period of six months and filled in the questionnaire both before and after this period. Correlations between the nutrient intake values from the food records and those from the food frequency questionnaires ranged from 0.33 for selenium to 0.68 for polyunsaturated fat. On the average, 40-45% of the subjects in the lowest and highest quintiles based on food records were in the same respective quintiles when assessed by the food frequency questionnaire, and 70-75% were in the two lowest and two highest questionnaire quintiles, respectively. The food frequency questionnaire and a quantitative food use questionnaire tested in the same study were compared. Use of these two instruments in large-scale epidemiologic studies is discussed.

Reproducibility and validity of dietary assessment instruments. I. A self-administered food use questionnaire with a portion size picture booklet

A self-administered food use questionnaire which included 276 food items and mixed dishes and a portion size picture booklet with 122 photographs was developed for a large lung cancer intervention trial among approximately 27,000 Finnish men aged 50-69 years. The reproducibility and validity of this questionnaire were studied from March to October 1984. In the reproducibility study, 121 men aged 55-69 years completed the questionnaire three times, at three-month intervals. The intraclass correlations varied from 0.56 for vitamin A to 0.88 for alcohol, with most falling between 0.60 and 0.70. In the validity study, 190 men of similar age kept food consumption records for 12 two-day periods, distributed evenly over a period of six months, and filled in the questionnaire both before and after this period. Correlations between nutrient intake values from the food records and the food use questionnaires ranged from 0.40 for selenium to 0.80 for alcohol. Among subjects who belonged to the lowest quintile on the basis of the food record measurement, an average of 51 per cent fell into the same quintile and 76 per cent fell into the lowest two quintiles when they were categorized on the basis of the food use questionnaire. Findings were similar for the upper tail of the distribution. These data indicate that the self-administered food use questionnaire is useful for measuring individual or group intakes for a variety of nutrients.

A data-based approach to diet questionnaire design and testing

A self-administered diet history questionnaire has been developed for epidemiologic and clinical use. Both the food list and the nutrient values to be associated with it were developed using dietary data from 11,658 adult respondents to the Second National Health and Nutrition Examination Survey (NHANES II). Food items were selected on the basis of their contribution to total population intake of energy and each of 17 nutrients in the NHANES II data, and represent over 90% of each of those nutrients. Associated nutrient composition values were determined from the NHANES II database using frequency of consumption data in that survey. Portion sizes to be associated with each food item were derived from observed portion size distributions in NHANES II, based on three-dimensional models. The resulting food list and its corresponding brief data base, when used to calculate nutrients from a diet record, yielded correlations of r greater than 0.70 with the more detailed method. Field administration produced mean values comparable to national data.

Nutrient sources in the American diet: quantitative data from the NHANES II survey. II. Macronutrients and fats

Dietary data from 11,658 adult respondents in the second National Health and Nutrition Examination Survey were used to provide quantitative information regarding the contribution of specific foods to the total population intake of the following nutrients: calories, protein, carbohydrate, total fat, saturated fat, oleic acid, linoleic acid, and cholesterol. The percentage of total nutrient intake which each food provides is presented for the top 50 contributors of each of these nutrients, as well as the proportion of the population consuming them. These data may provide a basis for the selection of foods to be included in dietary assessment instruments. They may also be useful to health care planners or nutrition educators.

Nutrient sources in the American diet: quantitative data from the NHANES II survey. I. Vitamins and minerals

Dietary data from 11,658 adult respondents in the second National Health and Nutrition Examination Survey were used to provide quantitative information regarding the contribution of specific foods to the total population intake of the following 10 nutrients: vitamin A, thiamine, riboflavin, niacin, vitamin C, iron, phosphorus, calcium, sodium, and potassium. Data are reported in the companion paper regarding the number of adults in the US population consuming each of 147 food items, representing all foods reported by these respondents. The percentage of total nutrient intake which each food provides is presented for the top 50 contributors of each of the nutrients listed above. Foods sometimes overlooked as important sources are found in some instances to be quantitatively important to population intake, such as spaghetti dishes as an independent source of carotenoids. These data should be useful to epidemiologists with a substantive interest in dietary etiologies or a methodological interest in the development of dietary assessment instruments. In addition, they may be useful to health care planners or nutrition educators.

Indicator foods for vitamin A assessment

Epidemiological interview studies examining the association between vitamin A and cancer at various sites have been hampered by restricted time available for interview; consequently, studies have included varying lists of food items or broad food groups, thus making comparability of results difficult. To identify a standardized list of indicator foods that adequately assess total vitamin A intake, we examined the 24-hour dietary recall of 13,201 adults who participated in the First National Health and Nutrition Examination Survey (NHANES I) from 1971 to 1974. Food items reportedly consumed were ranked by contribution to overall (aggregated) intake in various subpopulations by an index of vitamin A contribution, which reflected the frequency of consumption, portion size, and vitamin A concentration (IUs/100 g). A comparison of these ranks identified certain food items that had a relative contribution to vitamin A intake which varied by sex/race group, season of interview, age, or region of the country; income level had little effect on the food rankings. The top-ranking 50 foods were sufficient to correctly classify 80%-90% of the individuals into low-, moderate-, and high-consumer categories. The major contributing foods for any subpopulation examined included both retinol (e.g., dairy products, liver) and carotenoid sources of vitamin A (e.g., certain fruits and vegetables) in addition to items (e.g., mixed tomato and cheese dishes) not included in earlier questionnaire studies. Recommendations are made for future questionnaires designed to assess vitamin A.

Information for the spatial factor in Korte's 3rd Law of apparent motion

The experiments reported here show that Korte's space-time invariance equation governing perception of apparent motion is limited to situations in which metric or apparent separation of targets define but a single interval of space. Variation in interstimulus intervals and metric separation of targets did not influence the perception of apparent motion when the background array was structured to depict apparently equal intervals of space. These results provide a test of Koffka's and more recently Gibson's view that higher order properties of intervals of space specify the spatial factor in apparent movement.