An observational study was undertaken to examine if lawn pesticide use was significantly associated with bladder cancer.

An observational study was undertaken to examine if lawn pesticide use was significantly associated with bladder cancer. After adjusting for age, socio-economic status, and sex in a multivariate model, the investigators reported an effect size of 1.34, with a 95% confidence interval of 1.11-1.63. In the study, the investigators also determined that other factors (smoking, alcohol consumption, and family history of bladder cancer) were not significantly different between the cancer cases and non- disease controls. They concluded that these issues were not confounding influences on the study result. Therefore, can the study investigators conclude that confounding does not affect the validity of their study result? O Yes, because the investigators examined all potential confounding variables and adjusted for those considered to be important O No, because confounding may still exist from other, unknown confounders O Yes, because the study was statistically significant O No, because the investigators did not adjust for family history of bladder cancer, a known risk factor in other studies O Yes, because the investigators used proper methods in the design and analysis of the study

Consider the following table of results from a traditional case-control study. After the study, investigators found that the measurement instrument systematically overestimated the exposure values of the participants. Their finding was that 15% of all unexposed participants in the study, both cases and controls, were misclassified as exposed. This finding suggests that: Cases Controls Total 7 T i Exposed 350 200 550 Unexposed 150 100 250 Total 500 300 800 f i f f misclassification bias does not exist in the study misclassiflcation bias was due to random misclassiflcation misclassification bias is differential in the study misclassification bias in the study led to an odds ratio that is not possible to interpret for validity misclassification bias is non-differential in the study