Differences between quiz scores using a standardized z score. A difference score was created between the standardized quiz scores so that the degree to which the variability in each quiz affected the outcome would be the same. The difference score is standardized with a mean of 0 and a SD of 1.08. On the average, subjects in the MM group had lower scores on the second quiz (-.2061 SD), while those in the SNT group increased by about the same amount (.2093 SD). This represents about two-tenths of a SD and the difference was found to be significant (p = .027).