These effect codes eliminate all between-sample sources of variability and any between-sample differences are controlled even if specific measures regarding these differences are not available. Given the plethora of potential sources of between-sample heterogeneity that exist, controlling for all of these sources simultaneously can be both beneficial and efficient. Importantly, this method also provides a direct test of replication of findings across studies. Significant interactions between study and individual characteristics indicate a failure to replicate an effect across studies. This is a strong test of replication, testing not simply whether an effect is present in all studies but whether the magnitude of the effect is constant across studies.
