What type of study design allows for statements about causality?

The general goal of health psychology is to

a. encourage individuals throughout the world to get regular medical checkups. b. use psychological knowledge to promote wellness and positive health behaviors. c. use the principles of medicine to treat the physical body as separate from the psyche. d. eliminate the presence of Western scientific thinking in the medical community.

Juan experiences symptoms of sad mood, increased sleep, agitation, poor appetite, and concentration difficulties most of the day

Julia, on the other hand, has symptoms of loss of interest in activities, lethargy, increased appetite, feelings of worthlessness, and recurrent thoughts of death. What can be concluded regarding Juan and Julia? a) Both Juan and Julia have Bipolar disorder b) Juan has mania, whereas Julia has major depression. c) Both have major depression. d) Both have cyclothymic disorder.