In the article, “One’s Sex, Sleep, and Posttraumatic Stress Disorder”  I. Kobayashi et al. study the relationship between one’s sex, sleep patterns, and post-traumatic stress disorder (PTSD) after trauma exposure. The authors report that women have a higher lifetime prevalence of PTSD as well as a greater risk of developing PTSD following trauma exposure. Relationships between sleep and physical health have been documented in a number of studies, and the authors explore the possibility that disruptive sleep habits are common among people with PTSD and also a possible risk factor for the development of PTSD. A questionnaire of men and women with and without PTSD produced data on their sleep habits.

In Exercises, state whether the investigation in question is an observational study or a designed experiment. Justify your answer in each case.