No abstract

A large percentage of Canadian men 50 years of age or older experience symptoms commonly associated with BPH. The theoretical concept of irritative and obstructive symptom domains was supported partially by the cluster analysis. A clear typology of men with BPH symptoms could prove useful if treatments were found to be more effective for certain types of BPH symptoms. Thus these observations warrant further investigation into the differential effects of management approaches for BPH symptoms according to symptom clusters.

This study examined mortality to December 31, 1989 in a cohort of 2,222 males employed between 1947 and 1975 at a transformer manufacturing plant in Canada, where there had been extensive use of transformer fluid, some containing polychlorinated biphenyls (PCBs). A combined cohort list of 2,222 names was independently obtained from plant management and union officials. Mortality of 1,939 workers with known birthdates was ascertained by record linkage with the Canadian Mortality Data-base. Standardized mortality ratios (SMRs) for different criteria for acceptance of the death certificate link and for cohort membership (based on work history) ranged from .71-1.05. There was no significant increase in overall cancer deaths. The only significant site-specific increased mortality was pancreatic cancer (11 deaths), with SMRs ranging from 2.92-7.64 and higher mortality risk in those who entered the cohort prior to 1960. All but one of these deaths had a latency period of at least 10 years, and greatest SMRs were found in departments with the greatest exposure to transformer fluid. Several previous studies have found excess pancreatic cancers in association with oil exposures and electrical equipment manufacturing. The need to further investigate pancreatic cancer in transformer manufacturing and related exposures is evident.

In case-control studies, cases are sampled separately from controls. In such studies the primary analysis concerns the estimation of the effect of covariables on being a case or a control. To explore causal pathways, further secondary analysis could concern the relationships among the covariables. In this paper the validity of such secondary analysis is addressed. In particular, the use of multiple logistic regression in case-control studies where the dependent variable is not the case/control indicator is explored. It is shown that only under very restrictive conditions will sample regression coefficients correctly estimate their true value. In many situations, it may be valid to regress one covariable on others in the control group, but not in the case group or the combined sample. This principle is illustrated by a study of sexually transmitted disease in Kenya.