[Solved] What is premorbid IQ? Categories: Distinct groups or classifications into which data or objects can be organized. Normal Distribution: A bell-shaped frequency distribution curve that is symmetric about the mean, showing that data near the mean are more frequent in occurrence. Goodness-of-fit Test: A statistical test used to determine if a set of observed frequencies differs significantly from the expected frequencies. Test Statistic: A value calculated from sample data during a hypothesis test, used to make a decision about the null hypothesis.