You are doing a study on sleep deprivation on logical thinking. You take a sample of n = 25 individuals and deprive of them sleep so that they only get 4 hours of sleep for two nights. You then have them each solve a puzzle, and find that the mean time to solve the puzzle is M = 30 minutes. You know that for the population, the mean time to solve the puzzle is = 10 minutes and the standard deviation is = 20.

You want to answer the following research question: Does sleep deprivation have an effect on the amount of time it takes to solve this puzzle? What is the EFFECT SIZE, as measured by Cohen's d?