In this paper we perform a meta-analysis of the effects of monetary policies on output and prices. We use a sample of published papers on the effects of monetary policies in different countries. There is a large variation in the estimated effects of monetary policies on output and prices. We find that the use of different econometric methodologies is an important variable explaining these differences. In addition, we analyze the importance of macroeconomic variables. Thus we find that in countries with high inflation, the output effects of monetary policies are significantly reduced. A lot of variation in the estimated effects of monetary policies remains unexplained. More research will have to be done to understand these large differences.