A researcher studies 45 volunteer citizens from a small community and asks them about the amount of caffeine (in milligrams) they ingest before and after lunch each day, a phenomenon that imagine we know is normally distributed. Which of the following assumptions for the paired-samples t test is not met in this research design?
Select one:
a. All the assumptions are met.
b. The dependent variable is a scale variable.
c. The population is normally distributed.
d. Participants are randomly selected.