Association of semen quality and occupational factors: comparison of case-control analysis and analysis of continuous variables.

OBJECTIVE: To compare two statistical approaches, case-control and analysis of continuous parameters of semen, in examining the relationship between occupational exposures and male reproductive function.
DESIGN: Case-control study.
SETTING: Males providing semen samples at a university infertility clinic. PATIENT(S): Nonvasectomized males who provided at least one semen sample at an infertility clinic. MAIN OUTCOME MEASURE(S): Standard clinical semen analysis. RESULT(S): Analyses using a dichotomous dependent variable did not uncover significant associations between any occupational factor and infertility case status. However, linear models incorporating continuous variables identified a number of occupational factors that were associated with specific parameters of semen. A reduction in percentage of progressive sperm and an increase in percentage of coiled tail sperm defects in welders, compared with unexposed subjects, were found. Significant dose-response relationships between level of perceived job stress and percentage of progressive sperm, total motile count, morphology, abnormal heads, and coiled tail defects were found. CONCLUSION(S): The findings suggest that subtle changes in semen variables, possibly associated with workplace exposure, may be detected only with parametric analyses of continuous variables of semen.