ED t= nED2 - (ED)2 n-1 where D = difference between each person's scores; ED- the sum of those differences; ED2 = the sum of the differences squared; n = the number of pairs of scores. Perform a T-Test for Dependent Means Pretest Posttest Difference D2 8 9 10 3 10 Sum = Sum = Be sure to calculate the degrees of freedom, and use the column in Table B-2 for the usual .05 level of probability 14-15. T = Significant Y or N