I am carrying out a meta-analysis that looks at cognitive inhibition as an outcome. A wide range of assessment types can be used for this outcome and sometimes a study will include two or three that map onto this construct. I have created a moderator variable of outcome measure quality (i.e. range of poor [0] to good [2]) but am unclear if I simply want to choose the highest quality measure from each unique study or if I can include all of the different assessment types effects within a study and correct for this somehow in the analysis.