2. September 19, 2012 SYSTEMATIC REVIEWS

3. It is necessary, while formulating the problems of which in our advance we are to find the solutions, to call into council the views of those of our predecessors who have declared an opinion on the subject, in order that we may profit by whatever is sound in their suggestions and avoid their errors. Aristotle, De Anima, Book 1, chapter 2

4. Definitions Literature review A survey of previously published material Systematic review (aka research synthesis) Synthesis of previously published material to answer a research question Meta-analysis Quantitative procedures to combine the results of published research studies

6. Systematic Review Key differences from literature review: Integration of primary research studies Synthesis of those studies Seek to answer a research question Quantitative analysis (usually)

7. Importance of Systematic Review Since 1970s systematic review has become its own type of research Citations to systematic reviews over time:

8. Examples Problem: Hantavirus in the United States Literature review History of hantavirus in the United States Systematic review Are pet owners at lower risk for hantavirus infection? Meta-analysis Quantitative methods to analyze risk of hantavirus infection in pet owners vs non pet owners

9. Stages of Systematic Review 1.Define the Problem 2.Literature Search 3.Data Evaluation 4.Data Analysis 5.Interpretation of Results 6.Presentation of Results

11. Why conduct a systematic review? Synthesize knowledge Critically analyze a problem Create generalizations Identify and analyze central theories Identify limitations Resolve conflicts Identify central issues for future research

12. Terms to Consider Bias Grey literature Heterogeneity Representativeness Utility

13. Bias “if the sample of studies retrieved for review is biased, the validity of the results, no matter how systematic and thorough in other respects, is threatened” A bias prevents neutral review of information: Personal bias (due to author’s views) Publication bias (reporting of positive results) Language bias (excluding studies by language) Availability bias (readily available study results) Cost bias (inclusion of free or low cost studies)

14. Grey Literature Literature that is hard to retrieve Results of research not published Literature produced by government, academia, etc that with other goal than commercial publishing Will not be retrieved by traditional database search

15. Heterogeneity The extent to which observed effects differ from one another (the variability of the effect sizes in various studies in your systematic review) Systematic review pools data from many research studies These studies are inherently different Are the included studies similar enough to yield meaningful results when pooled?

16. Tests of Heterogeneity Cochran’s Q Weighted sum of squared differences in study effects Distributed as chi-squared statistic Informs of presence vs absence of heterogeneity I 2 Estimate of percent variability across studies Helps quantify degree of heterogeneity As I 2 increases, more heterogeneity exists

17. Representativeness How well included studies represent all studies Can we draw meaningful inferences using studies included in a review? Limitations: Types of studies that have been conducted Search methods – exhaustive? Accessibility of conducted studies Publication or reporting bias

18. Utility “fitness for some purpose or worth to some end” –Merriam Webster Dictionary Considers ultimate goal of the review What will the review add to the evidence database? What information to include Audience