You can use both the t statistic and the z statistic to test hypotheses about the mean of a population. The test that uses the t statistic is typically referred to as a t-test, while the test that uses z statistic is commonly called a z test.
Which of the following statements are true of the t statistic? Check all that apply.

a) If you know the population standard deviation, you should use the t statistic.
b) The t statistic could be considered as an estimated z statistic.
c) The t statistic provides a relatively poor estimate of z with small sample sizes.
d) The formula for the t statistic is t = (M - s) / sₘ.

With the exception of whether the population standard deviation is known, the necessary assumptions for hypothesis tests with the t statistic and with the z statistic are .