The range or spread of scores is defined as

A) the average difference.
B) the statistical significance.
C) variability.
D) a confounding variable.

The range or spread of scores refers to the extent of variability in a set of data. This means it represents how much the scores differ from each other, which is a measure of variability. Therefore, option C is the correct answer. Option A is incorrect because the average difference is referred to as the mean or standard deviation, which are different measures. Option B is incorrect because statistical significance relates to the likelihood of observing a particular result by chance alone, which is not relevant to the range. Option D is incorrect because a confounding variable is an extraneous variable that can influence the results, which is not a measure of spread or variability.