ESTIMATING THE EFFECT OF THE FILE DRAWER PROBLEM IN METAANALYSIS

Although meta-analysis appears to be a useful technique to verify the existence of an effect and to summarize large bodies of literature, th ere are problems associated with its use and interpretation. Amongst d ifficult ies is the ''file drawer problem.'' With this problem it is a ssumed that a certain percentage of studies are not published or are n ot available to be included in any given meta-analysis. We present a c autionary table to quantify the magnitude of this problem. The table s hows that distortions exaggerating the effect size are substantial and that the exaggerations of effects are strongest when the true effect size approaches zero. A meta-analysis could be very misleading were th e true effect size dose to zero.