I'm organizing a meta-analysis on performances with studies showing sometime positive and sometime negative estimates.
Sometime the result of the study is in a positive direction, with higher scores corresponding to better performance (e.g., number of tasks completed). Sometime the result of the study is in a negative direction, with lower scores corresponding to better performance (e.g., time to completion of the task).
How can I put together both types of studies? What kind of mathematical correction can I do?
I was thinking of estimating the effect size (in Hedges' g), then multiplying per -1 the positive-sided studies, so all studies will be in a negative direction. Is this a valid approach?