Selective reporting has been offered by critics as an explanation for the positive results reported by parapsychologists. Selective reporting is sometimes referred to as a "file drawer" problem, which arises when only positive study results are made public, while studies with negative or null results are not made public. Selective reporting has a compounded effect on meta-analysis, which is a statistical technique that aggregates the results of many studies in order to generate sufficient statistical power to demonstrate a result that the individual studies themselves could not demonstrate at a statistically significant level. For example, a recent meta-analysis combined 380 studies on psychokinesis, including data from the PEAR lab. It concluded that, although there is a statistically significant overall effect, it is not consistent and relatively few negative studies would cancel it out. Consequently, biased publication of positive results could be the cause.