Chapter 48 Lab 11 exercises

48.1 Exercise 1

Compute RT interference scores for the Stroop task.

48.2 Exercise 2

If your version of SPSS is like mine, one of the levels of measurement will be incorrect. Can you work out which one it is and why it is incorrect?

Hint 1

Levels of measurement are defined by the type of operations you can meaningfully perform on the data. For example, scale-level data should allow you to compute means, ordinal-level data to compute medians and categorical-level data to compute frequencies.

Hint 2

Is there a scale variable for which it would not make sense to compute a mean?


It’s the participant ID. This is certainly numeric (see Type), but it is not at scale level (or ordinal level, for that matter). It is a categorical variable. The reason is that assignment of IDs to participants is completely arbitrary. It does not indicate a more or less of something we measured. Participant 1 is not “better” than, say, Participant 89.