Methodological and Practical Challenges in Synthesizing Occupational Cancer Studies

Studies examining occupational exposures and cancer risk frequently report mixed findings; it is thus imperative for researchers to synthesize study results and identify any potential sources that explain such variabilities in study findings. However, when synthesizing study results using meta-analytic techniques, researchers often encounter a number of practical and methodological challenges. These challenges include (1) an incomparability of effect size measures due to large variations in research methodology; (2) a violation of the independence assumption for meta-analysis; (3) a violation of the normality assumption of effect size measures; and (4) a variation in cancer definitions across studies and changes in coding standards over time. In this paper, we first demonstrate these challenges by providing examples from a real dataset collected for a large meta-analysis project that synthesizes cancer mortality and incidence rates among firefighters. We summarize how each of these challenges has been handled in our meta-analysis. We conclude this paper by providing practical guidelines for handling challenges when synthesizing study findings from occupational cancer literature.