Calculating Z Tests and Difference Effects Group Size Mean Standard Deviation Sample 30 98 5 Population 600 95 4 Perform a Z Test: where = the mean of the sample; = population mean; and SEM is the Standard Error of the Mean. SEM= where = standard deviation for the population and n = size of sample. First figure out SEM; then, plug into the formula for a Z test. SEM = Z = Is that statistically significant? Y or N Then calculate the Effect Size: where d = Effect Size; again = the sample mean; = the population mean; and = the population standard deviation. d = Is it meaningful? Y or N