Bias arising in case-control studies from selection of controls from overlapping groups.

Three examples are used to demonstrate that the selection of controls from categories that overlap can lead to bias. Case-control studies that use friend controls and the practice of age-matching controls to cases within a specified number of years (caliper matching) are examples of the selection bias described in the paper. The bias resulting from the use of friend controls can be large and, since the use of friend controls is common, this source of bias is of considerable practical consequence.

Predictive values, relative risks, and overall benefits of high and low maternal serum alpha-fetoprotein screening in singleton pregnancies: new epidemiologic data.

In a prospective study of maternal serum alpha-fetoprotein screening for both high and low values, we assessed the overall predictive value, sensitivity, specificity and relative risks for congenital defects and complications of pregnancy. Among 13,486 women with singleton pregnancies interviewed at the time of screening (15 to 20 weeks of gestation), 3.9% had high and 3.

A strengthening programme for weak associations.

The strength of a causal association depends on the relative prevalence of other component causes for the same disease. Weak associations may sometimes be strengthened by restricting attention to people at low risk. This technique may lead to fewer subjects to study, but nevertheless may provide more information by which to evaluate a causal relation.

Chemical quality of maternal drinking water and congenital heart disease.

We undertook a case-control study to investigate the association between chemicals in maternal drinking water consumed during pregnancy and congenital heart disease in the offspring. Two hundred and seventy affected children and 665 healthy children were enrolled in the study. Information on contaminant levels in maternal drinking water was available from records of routine water analysis of samples taken from public taps in the communities where the mothers resided during pregnancy.

Use of oral and topical agents for acne in pregnancy.

Dermatologists frequently are consulted by a pregnant patient or a woman of childbearing age who desires acne therapy. Because there are no published studies in which women took acne medications throughout pregnancy, information about safety must be obtained indirectly from studies in which the agents were taken for another indication during some portion of pregnancy. Oral tetracycline is associated with maternal liver toxicity and deciduous tooth staining in the infant, and tetracycline occasionally has been associated with other congenital anomalies.

The diagnosis and treatment of chancroid.

Chancroid, a disappearing disease in the United States, was reintroduced into the country in 1980 by immigrants from the Caribbean, Mexico, and Southeast Asia. Point epidemics resulted, each of them associated with prostitution. During the 4-month period between March 1 to June 30, 1985, forty-five patients were diagnosed and treated in Massachusetts, thirty-seven from Boston alone.

Congenital heart disease in relation to maternal use of Bendectin and other drugs in early pregnancy.

To clarify the association of Bendectin and other drugs used in early pregnancy with the occurrence of congenital heart disease, we interviewed 298 mothers of children with congenital heart disease and 738 mothers of healthy controls. Differential recall of drug use by mothers of affected children and mothers of controls was evaluated by comparison of information collected by interview with that recorded in the prenatal record. Data derived from maternal interviews were generally consistent with the record data.

Epidemiology of squamous cell cancer of the head and neck.

Epidemiologic investigations have been instrumental in identifying numerous factors associated with the development of cancer. Tobacco and alcohol are unquestionably the major risk factors for squamous cell carcinoma of the head and neck region. Diet appears to play a role in the development of these cancers, as nutritional deficiencies have been found to increase risk.

Pyloric stenosis and maternal Bendectin exposure.

As part of a long-term follow-up of structural disorders present at birth or shortly thereafter in infants born at Group Health Cooperative of Puget Sound, all infants with a diagnosis of pyloric stenosis born between July 1, 1977 and June 30, 1982, were identified. Automated pharmacy profiles were examined to determine whether an association between maternal Bendectin use in the first trimester and infantile hypertrophic pyloric stenosis existed. Among the 3,835 women exposed to Bendectin while pregnant, in this group of 13,346 births, 13 had infants who developed pyloric stenosis, and among the 9,511 women not exposed, 13 had infants who developed pyloric stenosis, resulting in a risk ratio estimate of 2.

Work-related risk factors for laryngeal cancer.

The authors conducted a case-control study to identify employment-related risk factors for laryngeal cancer. Richmond County, Georgia, and the contiguous counties were chosen as the study area because the 1950-1969 laryngeal cancer mortality rate for white males in Richmond County was almost double the corresponding rate for the entire United States, and because a large proportion of the working population was employed in industries for which excess risk among workers had been reported. All persons with newly diagnosed squamous cell carcinoma of the larynx treated in the area hospitals were identified.

Projections of asbestos-related disease 1980-2009.

Approximately 19,000 cases of mesothelioma and 55,000 cases of lung cancer will arise in U.S. men with histories of nontrivial occupational exposure to asbestos.

Vaginal spermicides and gonorrhea.

All positive cultures for neisseria gonorrhoeae recorded from Dec 20, 1978, through Dec 31, 1980, for women born between 1940 and 1960 were identified among members of Group Health Cooperative of Puget Sound, Seattle, and rates of gonorrhea were calculated for recent oral contraceptive users, recent vaginal spermicide users, and women with surgical sterilization. The risk ratio (RR) estimate, based on the included population, for spermicide users compared with all others was 0.23 (90% confidence interval [Cl], 0.

An independent analysis of the National Cancer Institute study on non-nutritive sweeteners and bladder cancer.

We evaluated the possible relation between use of non-nutritive sweeteners and bladder cancer using data obtained from the National Cancer Institute Bladder Cancer Study under the Freedom of Information Act. In the general study group, there was no evidence for an association between non-nutritive sweeteners and bladder cancer. Control for a variety of factors through multivariate techniques diminished the plausibility of earlier interpretations of these data, which had raised the possibility that certain subgroups of users or non-nutritive sweeteners might be at an increased risk for bladder cancer.