On tests of the overall treatment effect in meta-analysis with normally distributed responses

For the meta-analysis of controlled clinical trials or epidemiological stud ies, in which the responses are at least approximately normally distributed , a refined test for the hypothesis of no overall treatment effect is propo sed. The test statistic is based on a direct estimation function for the va riance of the overall Treatment effect estimator. As outcome measures, the absolute and the standardized difference between means are considered. In s imulation studies it is shown that the proposed test keeps the prescribed s ignificance level very well in contrast to the commonly used tests in the f ixed effects and random effects model, respectively, which can become very liberal. Furthermore, just for using the proposed test it is not necessary to choose between the fixed effects and the random effects approach in adva nce. Copyright (C) 2001 John Wiley & Sons, Ltd.