A systematic review is a research method which summarizes the results of all relevant studies through systematic and scientific processes in order to answer a specific research question. For this reason, a systematic review is one of the most frequently used methods in assessing the effectiveness and safety of interventions as a part of Health Technology Assessment [HTA].

However, systematic reviews are subjected to reporting bias because the methods are fundamentally based on the studies which are already existed. Among various kinds of reporting bias, publication bias leads to overestimation of effect size in systematic reviews with meta-analyses, which could affect the credibility of study results. Therefore, it is important to investigate and adjust publication bias when meta-analyses are conducted in systematic reviews.

The purposes of this study are followed:

A. Introducing various methods of detecting small study effect & publication bias, and methods of adjusting publication bias through reviewing major text books and updated relevant studies

B. Investigating the current status of meta-analysis studies exploring small study effect & publication bias from major journals

C. Exploring small study effect & publication bias to compare the results reported by authors and the adjusted results by the current study and to investigate how the effect estimates in meta-analyses could change between the results