• The Z-test is a statistical test to determine if two population means differ when the variances are known and the sample size is large.
  • A z-test is a hypothesis test in which the z-statistic follows a normal distribution.
  • A z-statistic or z-score is a number representing the result of a z-test.
  • Z-tests are closely related to t-tests, but t-tests are best done when the experiment has a small sample size.
  • Z-tests assume that the standard deviation is known, while t-tests assume that it is unknown.