This simulation demonstrates the t test for correlated observations. When you click the "sample" button, 12 subjects with scores in two conditions are sampled from a population. Each population is normally distributed with a standard deviation of 4. The mean for condition 1 is 15 and the mean for condition 2 is 13. The initial population correlation between conditions is 0.5, although you can change that.

The data from the sample of 12 subjects is graphed with a line connecting the two data points for a subject. The difference scores (Condition A - Condition B) are computed and graphed as well as shown in a table.

At the bottom of the display is shown the mean difference score, the standard deviation of the difference scores, the standard error of the mean difference score, the value of t, and the value of p.