Hello. I study Psychology in the University of Paris-VIII(Master 2 in developmental Psychology). I work on the school engagement of different groups. I have some questions about how to interprate the the needed sample size and the d (Cohen) effect. For example, an online calculator, says me that if I want a d=.80 , a power = .80, and a alpha = .05, in the case of an U test, I need 68 subjects (ratio 0,38) .. But when i make a post-hoc analyse on the average score for the two groups, d=0,343 ... Could you help me to interprate this results

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