Risk of Bias Assessment
Risk of bias assessment, otherwise known as critical appraisal or quality assessment, is an essential step in conducting a systematic review. It involves grading each study based on a set of pre-defined criteria to assess the quality of the evidence that each study presents.
Different sets of criteria and grading methods are available for different kinds of studies. In my protocol, I stated the risk of bias tools I would be using. I chose the Newcastle-Ottawa Scale (NOS) for case control and cohort studies (I also slightly modified the cohort criteria to be used for cross-sectional studies), ToxRTool (Toxicological Data Reliability Assessment Tool) for in vitro studies, and JBI’s critical appraisal tool for systematic reviews for systematic reviews (and other kinds of reviews).
With each study, I go through the criteria of the tool corresponding to the study design. The criteria is a yes/no checklist or a set of questions. A point is either awarded or not awarded for each question. For example, here is the first question from the NOS for cohort studies (the most common study design so far):
1) Representativeness of the exposed cohort
a) truly representative of the average exposed person undergoing IVF (point)
b) somewhat representative of the average exposed person undergoing IVF (point)
c) selected group of users eg nurses, volunteers (no point)
d) no description of the derivation of the cohort (no point)
I would look at the description of the participants who were exposed to the toxin in the methods section of the study and record whether the study met the criteria for a point or not in my spreadsheet. After I go through all the criteria, I add up the points, which correspond to a certain risk of bias score for the study.
Next week, I think I’ll begin preparing my presentation and putting together the final paper. For the paper, I’ll need to splice the already-written sections of my paper together in one document (abstract, introduction, methods, and results), write my preliminary discussion and conclusion sections, arrange my citations, and make any necessary edits.
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