Volunteers for a Human Performance Study Were Randomly Divided into Two

Multiple Choice

Volunteers for a human performance study were randomly divided into two groups. The first group had their flexibility measured in the morning after a short meditation session while the second group had their flexibility measured in the afternoon with no previous meditation session. The flexibility scores of the two groups were compared.
An example of a lurking variable that might affect the results of this study is:

A) whether the volunteer had a meditation session.
B) the time of day the test was administered.
C) whether the volunteer practiced yoga.
D) whether the volunteer was being paid to participate in the study.