The one-sample Z test is used when we want to know whether our sample comes from a particular population. For instance, we are doing research on data collected from successive cohorts of students taking the Elementary Statistics class. We may want to know if this particular sample of college students is similar to or different from college students in general. The one-sample Z test is used only for tests of the sample mean. Thus, our hypothesis tests whether the average of our sample (M) suggests that our students come from a population with a know mean (m) or whether it comes from a different population.
The statistical hypotheses for one-sample Z tests take one of the following forms, depending on whether your research hypothesis is directional or nondirectional. In the equations below m1 refers to the population from which the study sample was drawn; m is replaced by the actual value of the population mean.