Editing Meta-analysis (section)

===Problems related to studies not reporting non-statistically significant effects===

Studies often do not report the effects when they do not reach statistical significance.<ref>{{Cite journal |last1=Schober |first1=Patrick |last2=Bossers |first2=Sebastiaan M. |last3=Schwarte |first3=Lothar A. |date=2018 |title=Statistical Significance Versus Clinical Importance of Observed Effect Sizes: What Do P Values and Confidence Intervals Really Represent? |journal=Anesthesia & Analgesia |language=en |volume=126 |issue=3 |pages=1068–1072 |doi=10.1213/ANE.0000000000002798 |issn=0003-2999 |pmc=5811238 |pmid=29337724}}</ref> For example, they may simply say that the groups did not show statistically significant differences, without reporting any other information (e.g. a statistic or p-value).<ref>{{Cite journal |last1=Gates |first1=Simon |last2=Ealing |first2=Elizabeth |date=2019 |title=Reporting and interpretation of results from clinical trials that did not claim a treatment difference: survey of four general medical journals |journal=BMJ Open |language=en |volume=9 |issue=9 |pages=e024785 |doi=10.1136/bmjopen-2018-024785 |issn=2044-6055 |pmc=6738699 |pmid=31501094}}</ref> Exclusion of these studies would lead to a situation similar to publication bias, but their inclusion (assuming null effects) would also bias the meta-analysis.