when conducting a z test the null and alternative hypotheses and alpha level should be stated the z score also called a test statistic should be calculated and the results and conclusion stated a z statistic or z score is a number representing how many standard deviations above or below the mean population a score derived from a z test is 
examples of tests that can be conducted as z tests include a one sample location test a two sample location test a paired difference test and a maximum likelihood estimate z tests are closely related to t tests but t tests are best performed when an experiment has a small sample size also t tests assume the standard deviation is unknown while z tests assume it is known if the standard deviation of the population is unknown the assumption of the sample variance equaling the population variance is made the z score is calculated with the formula 