A researcher uses a repeated-measures design to compare individuals' performance before treatment with their performance after treatment.If all the participants show improved performance of 8 or 9 points after treatment,what should the researcher find?
A)The sample mean difference is near zero.
B)The t statistic is near zero.
C)The variance of the difference scores is near zero.
D)None of the other options is correct.

Question

Quizplus · Accepted Answer

If all participants show the same improvement, the variance of the difference scores will be very low, approaching zero. This is because there are no individual differences to account for in the change scores, so the differences will be very consistent. Therefore, the researcher should find that the variance of the difference scores is near zero. The sample mean difference will also be 8 or 9 points, but this does not necessarily mean that the mean is near zero, as the starting point could have been much lower or higher. The t statistic will depend on the sample size and standard deviation, so it is not necessarily near zero either.

A Researcher Uses a Repeated-Measures Design to Compare Individuals' Performance