"Fading of Reported Effectiveness" Bias: Longitudinal Meta-Analysis of Randomized Controlled Trials.

Meta-analyses have become an instrument that is fundamental to the idea of best medical care. Meta-analyses combine the results of a large number of randomized controlled trials (RCTs) on a certain topic to gain more significant results. Should the reported effect size of RCTs change with time, the result of a meta-analysis would depend on when it was performed. Thus, the validity of a meta-analysis could be impaired. [ABSTRACT FROM AUTHOR]