A researcher reports a significant treatment effect with t24

A researcher reports a significant treatment effect with t(24) = 3.04. How many scores were in the sample?

Solution

Since this was a t-test, we should assume that mean and variance both were unknown. Since the test involves the testing of mean which is unknown, we need to estimate the mean from the sample. This estimation results in reduction of degrees of freedom by 1. As the reported value was t(24), we conclude there was 24+1=25 observations. 1 df was reduced due to estimation of unknown mean.