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3. Contacting of authors modified crucial outcomes of systematic reviews but was poorly reported, not systematic, and produced conflicting results;Meursinge Reynders;J Clin Epidemiol,2019
4. Systematic reviewers commonly contact study authors but do so with limited rigor;Mullan;J Clin Epidemiol,2009
5. Evaluating the effectiveness, efficiency, cost and value of contacting study authors in a systematic review: a case study and worked example;Cooper;BMC Med Res Methodol,2019