APA Dictionary of Psychology

a statistical procedure used to determine whether there is a significant difference between the observed mean of a sample and the known or hypothetical mean of the larger population from which the sample has been randomly drawn. In the single-sample t test, one calculates a t value using (a) the mean of the sample (observed average); (b) the mean of the population (known or theoretically expected average); (c) the standard deviation of the sample; and (d) the total number of sample observations taken. The t value obtained is then compared to a standard table of values, arranged by sample size, to determine whether it exceeds the threshold of statistical significance. Also called one-sample t test.