ISSN:1044-3983    

出版商:OVID    

年代:1994

数据来源: OVID

ISSN:1044-3983    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

A large body of experimental data and several recent epidemiologic studies indicate that aspirin use may decrease cancer risk. The experimental studies found effects at many anatomic sites, whereas the epidemiologic studies saw the greatest effect on mortality from digestive cancers. To provide further human data, we examined the association between aspirin use and cancer risk using data from the National Health and Nutrition Examination Survey I (NHANES I) and the NHANES I Epidemiologic Follow-up Studies (NHEFS). Characterization of aspirin use was based on questions in the baseline interview asking whether subjects used aspirin during the previous 30 days. Data were available from 12,668 subjects age 25–74, at time of initial examination for NHANES I, who were followed for an average of 12.4 years. Among these subjects, 1,257 were diagnosed with cancer more than 2 years after their NHANES I examination. Incidence of several cancers was lower among persons who reported aspirin use: the incidence rate ratios (and 95% confidence intervals) for all sites combined were 0.83 (0.74–0.93), lung cancer 0.68 (0.49–0.94), breast cancer in women 0.70 (0.50–0.96), and colorectal cancer in younger men 0.35 (0.17–0.73). These findings were not readily explained by potentially confounding factors. The data suggest an association between aspirin consumption and decreased cancer incidence at several cancer sites.

ISSN:1044-3983    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

To examine the relation between adverse pregnancy outcomes and work in cosmetology during pregnancy, we conducted a mail survey in North Carolina among 8,356 licensed female cosmetologists 22–36 years of age. We identified pregnancies between 1983 and 1988 by a brief screening questionnaire, followed by a more detailed mail questionnaire. Seventy-four per cent of eligible cosmetologists responded to each inquiry. We restricted the main analysis to 96 cosmetologists with a spontaneous abortion and 547 cosmetologists with a single live-birth who worked full-time in cosmetology or in other jobs during the first trimester of pregnancy. With adjusted odds ratios ranging from 1.4 to 2.0, we found associations between spontaneous abortion and the number of hours worked per day in cosmetology, the number of chemical services performed per week, the use of formaldehyde-based disinfectants, and work in salons where nail sculpturing was performed by other employees. We found no important associations among full-time cosmetologists who performed few chemical services and among cosmetologists who worked less than 35 hours per week.

ISSN:1044-3983    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

In conducting reviews or meta-analyses, epidemiologists frequently must reconcile conflicting results. This paper addresses heterogeneity in nonexperimental studies. The emphasis is on simple exploratory methods rather than formal approaches. Five examples illustrate how quantitative concordance among studies is possible, even when measured effects appear discrepant. The examples concern ethylene oxide and leukemias, methylene chloride and liver cancer, saccharin and bladder cancer, prenatal lead exposure and birthweight, and aspirin and bleeding tendencies in labor and delivery. Data examined here indicate that differences in dose levels frequently explain heterogeneous effect measures, often outweighing other sources of variability among studies. We present simple methods for combining dose information from the study of interest with dose-response data from other epidemiologic studies or animal studies to derive plausible hypothesized effect levels. These plausible effect sizes are the measures of association that would be predicted, for the actual exposures, by extrapolating from other studies with possibly differing exposure levels. Post hoc power calculations and comparisons of confidence intervals for overlap to reconcile “positive” and “null” studies may be misleading, since these approaches assume a uniform true association obscured by random fluctuations only. Whenever it can be estimated, a plausible effect size should be the starting point to assess findings of either positive or null studies. Without such calculations, comparisons among conflicting studies may not be meaningful.

ISSN:1044-3983    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

This paper focuses on some statistical considerations in the estimation of dose-response in case-control studies when the exposure variables are continuous measurements. The first point is that the effects of differential variability in the exposure distributions over cases and controls cannot be differentiated from a true quadratic risk model. The second point is that when dealing with variables where zero denotes no exposure, it is important to treat the unexposed subjects separately from those who were exposed. Failure to do so can lead to differential variability among cases and controls and the resulting confounding with a quadratic risk model. Both of these points are illustrated by an example.

ISSN:1044-3983    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

We conducted a simulation study to examine the performance of confidence intervals when multiplicative and additive rate (Poisson regression) models are fit to follow-up data, but the model form may be misspecified. Data were generated from over 129,000 different population structures that ranged from sub-additive to supra-multiplicative. When a multiplicative model was fit, all of the confidence intervals that we examined performed well as interval estimators of the asymptotic means of the point estimators, even when the correct model form was not multiplicative. When an additive model was fit, (1) only the likelihood ratio interval and the score interval with expected information consistently performed well, and they consistently performed better than any of the Wald intervals that we examined; (2) Wald intervals performed better when calculated with observed information rather than with expected information; and (3) Wald intervals with expected information performed better when the information matrix was evaluated at the restricted maximum likelihood estimate rather than the unrestricted maximum likelihood estimate.

ISSN:1044-3983    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

We used data from a hospital-based case-control study of tobacco-related cancers to test the hypothesis that smoking mentholated cigarettes increases the risk of cancer of the oral cavity and pharynx, a cancer with a 50% higher incidence in black Americans compared with whites. Detailed information on smoking habits and other variables, obtained in personal interviews, was available for 194 male and 82 female newly diagnosed, histologically confirmed cases of oropharyngeal cancer and 845 male and 411 female controls, all of whom were current smokers. In univariate, stratified, and multivariable analyses involving all cases and controls, menthol was not a risk factor for cancer. The odds ratio, adjusted for covariates, for smoking mentholated cigarettes for ≥ 15 years relative to smoking nonmentholated cigarettes only was 0.9 (95% confidence interval = 0.5–1.6) in males, and 0.7 (95% confidence interval = 0.5–1.7) in females. In analyses by subsite, menthol use was positively associated only with cancer of the pharynx in males, although the magnitude of the association was small. These results indicate that use of mentholated cigarettes is unlikely to be an important independent factor in oropharyngeal cancer.

ISSN:1044-3983    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The “healthy worker survivor effect” describes a continuing selection process such that those who remain employed tend to be healthier than those who leave employment. In an analysis of exposure-response patterns in an occupational study, the healthy worker survivor effect generally attenuates an adverse effect of exposure. In practical terms, such attenuation will be more problematic when evaluating subtle rather than strong associations. The use of an internal referent does not guarantee elimination of this effect, since by definition, it manifests within an occupational cohort. Although documented over 100 years ago, there is little consensus regarding the most appropriate method to control for the healthy worker survivor effect. Four methods have been proposed for its control: (1) restriction of the cohort to survivors of a fixed number of years of follow-up, (2) lagging the exposure to exclude recent exposure incurred by those who remained on the job, (3) adjusting for employment status as a confounder, and (4) treating the healthy worker survivor effect simultaneously as an intermediate and confounding variable by means of the G-null test or its extension, Gestimation analysis, using structurally nested failure time models. This paper reviews the concept of the healthy worker survivor effect and the four methods to control for it.

ISSN:1044-3983    

出版商:OVID    

年代:1994

数据来源: OVID

摘要:

The decline in ischemic heart disease (IHD) mortality in the United States in recent years is thought to have contributed to increases in cancer mortality. To estimate the interrelation between these competing causes of death between 1970 and 1988, I constructed a hypothetical population schedule by assuming that age-specific IHD mortality risks had not declined. The difference between the actual population and the hypothetical population represents persons who did not die from IHD and were thus available to die from cancer. Using observed age-specific cancer risks over the entire interval, 153,207 of the 7,649,058 cancer deaths (2.0%) in persons age 20–85 years occurred in IHD survivors; in 1988, 24,053 of the 482,490 cancer deaths (5.0%) occurred in IHD survivors. Among 55 to 85 year olds in 1988, IHD survivors accounted for 5.5% of the cancer deaths. Alternative assumptions about the susceptibility of IHD survivors to cancer have little impact on the contribution of IHD survivors to cancer deaths. Results from a separate analysis demonstrated that the proportional contribution of true cancer risk to the increase in cancer cases tripled in the interval 1970–1988 compared with the interval 1930–1970. These observations indicate that the contribution of the IHD mortality decline to the increase in cancer mortality has been small and does not account for the increasing age-specific risks for cancer among older persons.

ISSN:1044-3983    

出版商:OVID    

年代:1994

数据来源: OVID