Colonoscopy with biopsy or polypectomy is associated with increased risk for complications. Perforation may also occur during colonoscopies without biopsies.

The authors explored two methodological issues in the estimation of smoking-attributable mortality for the United States. First, age-specific and age-adjusted relative risk, attributable fraction, and smoking-attributable mortality estimates obtained using data from the American Cancer Society's second Cancer Prevention Study (CPS II), a cohort study of 1.2 million participants (1982-1988), were compared with those obtained using a combination of data from the National Mortality Follow-back Survey (NMFS), a representative sample of US decedents in which information was collected from informants (1986), and the National Health Interview Survey (NHIS), a nationally representative household survey (1987). Second, the potential for residual confounding of the disease-specific age-adjusted smoking-attributable mortality estimates was addressed with a model-based approach. The estimated smoking-attributable mortality based on the CPS II for the four most common smoking-related diseases-lung cancer, chronic obstructive pulmonary disease, coronary heart disease, and cerebrovascular disease-was 19% larger than the estimated smoking-attributable mortality based on the NMFS/NHIS, yet the two data sources yielded essentially the same smoking-attributable mortality estimate for lung cancer alone. Further adjustment of smoking-attributable mortality for disease-appropriate confounding factors (education, alcohol intake, hypertension status, and diabetes status) indicated little residual confounding once age was taken into account.

Public concern exists about the potential for reproductive damage that may result from exposures to environmental contaminants. Therefore, the authors sought to determine if there was an association between a child's congenital malformation or a child's lowered weight at birth and his or her mother's residence in a census tract where a site of environmental contamination had been documented. Exposure designations were derived from existing sources of information. Except for an elevated risk (odds ratio = 1.5) for infants with malformations of the heart and circulatory system, this investigation did not reveal increased risks for most malformations or for lowered birthweight among babies born to women who lived in these census tracts. Methodologic issues inherent to investigations that rely on existing data sources are discussed.