A one sample t-test (or single sample t-test) is used to compare the mean of a single sample of scores to a known or hypothetical population mean. So, for example, it could be used to determine whether the mean diastolic blood pressure of a particular group differs from 85, a value determined by a previous study. The example below shows the results of a t-test with a hypothesized (or population) mean of 10, a sample (or observed) mean of 12, a sample (or observed) standard deviation of 25, and a sample size (or number of observations) of 25.

A one sample t-test compares the mean (M) of a single sample of scores to a known or hypothetical population mean (m). This means you need to input the value of your known (or hypothetical) mean (m) and your sample scores (likely you’d already worked that out!).