# How to work out Effect Size for a MANOVA using G*Power

I'm using G*Power to work out how many participants I need. I'll be using a MANOVA, I have two independent variables (Male and Female) and they will be answering 13 different questionnaires so 13 dependent variables. I put this data into G*Power and its telling me I only need 14 participants but I think that is too small?

If you choose as test family F tests and as statistical test MANOVA: Global effects. You can choose as Type of power analyis A priori: Compute required sample size - given alpha, power, and effects size. Depending on the Effect size, alpha and power you would like to achieve you obtain the required sample size (with 2 for the number of groups, and 13 for the response variables). Of course the effect size, etc. are up to you to decide and should be based, among other things, on theory!