Abstract
This paper examines sources of potential bias in systematic reviews and meta-analyses which
can distort their findings, leading to problems with interpretation and application by practitioners
and policymakers. It follows from an article that was published in the Canadian Journal of
Communication in 1990, “Integrating Research into Instructional Practice: The Use and Abuse of
Meta-analysis,” which introduced meta-analysis as a means for estimating population parameters
and summarizing quantitative research around instructional research questions. This paper begins
by examining two cases where multiple meta-analyses disagree. It then goes on to describe
substantive and methodological aspects of meta-analysis where various kinds of bias can
influence the outcomes and suggests measures that can be taken to avoid them. The intention is
to improve the reliability and accuracy of reviews so that practitioners can trust the results and
use them more effectively.