why is the z t test used what is z-test vs t-test what are the assumptions used to do the t-test what does the standard t-test assume what is the difference between the t- and z-test what is the function of z-test what is the difference between t and z test what is the t test of a z which is better z or t test how is the variance compared under an t-test? what is the difference between a z and a t and compare mean what is z vs t test difference between a z & t test and an alternative t test to compare difference between z and t what is the z versus t test and t test what is the t test? what is a z test what is the t test used for in an experiment? why do we perform a t test is m a normal distribution