z test Why calculate z by subtracting the population mean and dividing by the population standard deviation? To calculate the probability of an observed value being as high as that we find, or higher, we compare it to possible values assuming the null hypothesis is true Where do we get these possible values? We know that a sampling distribution of the mean will approach normal with increasing n: that’s the overall shape The distribution depends on the values of the mean and the standard deviation Normal distribution mean=10, sd=1, n=10k z density 0.0 0.1 0.2 0.3 0.4 7 8 9 10 11 12 13