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.
This experiment was not double-blind because:
A) volunteers were allowed to keep their eyes open while having their flexibility measured.
B) the volunteers knew the whether they had meditated before having their flexibility measured.
C) some of the volunteers stretched before they went to the study location.
D) volunteers were randomized into the two groups.

Question

Quizplus · Accepted Answer

A study is double-blind when neither the participants nor the experimenters know which group is receiving the treatment or intervention. In this case, the volunteers were aware of whether they had the meditation session or not, so the study is not double-blind.

Volunteers for a Human Performance Study Were Randomly Divided into Two