Rebekah is interested in studying whether people report different levels of happiness (as reported on a 7pt Likert scale) before and after a meal. She obtains a random sample of 28 individuals and finds that happiness scores consistently increase across all participants. Which of the following would she observe in her difference scores?

A) Not enough information to determine

B) A small variance

C) A large variance

D) A small mean difference

E) A large mean difference