Personal privacy and public health: potential impacts of privacy legislation on health research in Canada.

Despite variation in Canadian privacy laws between provinces and territories, increasing legislative protection of personal privacy has imposed restrictions on health research across the country. The effects of these restrictions on patient recruitment include increased study costs, durations, and decreased participation rates. Low participation rates can jeopardize the validity of research findings and the accuracy of measures of association by introducing non-response, or participation bias. We constructed simulations to assess potential effects of non-response bias on the accuracy of measures of association in a hypothetical case-control study. Small biases that alter the probability of selecting an exposed case can lead to dramatic inflation or attrition of the odds ratio (OR) in case-control studies. ORs are more unstable and subject to error when the true probability of selecting an exposed case is greater, such that strong positive associations are subject to error even at low levels of bias. Well-powered, population-based epidemiological research is a cornerstone of public health. Therefore, when weighing the benefits of protecting personal privacy, the benefits of valid and robust health research must also be considered. Options might include special legislative treatment of health research, or the use of an "opt-out" (vs. the current "opt-in") construct for consent in confidential research.