Systematic reviews of research to assess causation: a guide to methods and application

This chapter describes the basic steps in a systematic review to evaluate causality. These steps are illustrated using a published review concerning the hypothesized mechanism by which homocysteine could lead to preeclampsia. The first and most important step is to specify the problems to be addressed in the form of well-structured questions (Step 1). This step is pivotal as all other aspects of the review follow directly from these questions. The next step is to conduct a thorough literature search to identify studies with the potential to be relevant to the questions you have posed (Step 2). This is necessary to make the review systematic. The third step involves assessing the quality of the relevant studies (Step 3). Furthermore, the study characteristics and results are summarized and any differences between studies are explored (Step 4). Metaanalysis, where possible, should be employed to collate results. Finally, interpretation of the results allows recommendations for practice to be made, in conjunction with discussion of the relevance of the findings (Step 5).