Treatments for depression in bipolar disorder (BD) are far less developed than for unipolar major depressive disorder. New experimental approaches have been emerging recently, including use of the dissociative anesthetic ketamine. To study the effectiveness of this new experimental treatment, 2 psychiatrists decide to conduct 2 separate studies to compare treatment outcomes between patients receiving ketamine and patients receiving the standard treatment for BD. Study A, by the first psychiatrist, identifies 25 patients who have been on each of these treatments for BD for at least 6 months. Study B, by the second psychiatrist, randomly assigns 25 patients to each treatment and evaluates treatment outcomes after 6 months. Which of the following best describes each of these 2 studies?

Question

Treatments for depression in bipolar disorder (BD) are far less developed than for unipolar major depressive disorder.  New experimental approaches have been emerging recently, including use of the dissociative anesthetic ketamine.  To study the effectiveness of this new experimental treatment, 2 psychiatrists decide to conduct 2 separate studies to compare treatment outcomes between patients receiving ketamine and patients receiving the standard treatment for BD.  Study A, by the first psychiatrist, identifies 25 patients who have been on each of these treatments for BD for at least 6 months.  Study B, by the second psychiatrist, randomly assigns 25 patients to each treatment and evaluates treatment outcomes after 6 months.  Which of the following best describes each of these 2 studies?

Quizplus · Accepted Answer

Explanation: Although the study design of each of these 2 studies is not fully described, some details can be inferred: Study A selects patients who have already been either on ketamine or standard treatment for bipolar disorder (BD) for at least 6 months. Therefore, participants are not randomly assigned to treatments, and researchers are passively observing the effect of these 2 treatments in an uncontrolled setting. Study B randomly assigns patients to either ketamine or standard treatment for BD, and researchers are actively observing the effect of these 2 treatments in a controlled setting. The random assignment of treatment to participants is the most evident difference between the 2 study designs among the answer choices; this is also one of the main differences between observational and experimental studies. In observational studies (eg, case series, case-control, cohort, cross-sectional studies), researchers do not assign participants to the intervention or control groups and only observe the subjects passively. This differs from experimental studies (eg, completely randomized, randomized block), in which researchers randomly assign participants to groups and monitor the result of a specific, randomly assigned intervention. In this case, Study A is an observational study in which the effects of naturally occurring exposures (ie, treatments for BD) are observed and compared between 2 groups of patients, whereas Study B is a randomized clinical trial in which the effects of randomly assigned treatments are monitored and compared between 2 groups of patients (Choice D). (Choices A and B) Some observational study designs (eg, case-control and cohort studies) and most experimental designs include a control group to evaluate the effects of a risk factor or treatment among groups. In this case, Study A is an observational study that evaluates the effect of a treatment (ie, ketamine) by comparing it to a control group (ie, standard treatment for BD). (Choice C) Follow-up periods are not exclusive to observational cohort or longitudinal designs; almost all experimental designs include a follow-up period. Educational objective: In observational studies, researchers observe participants and measure outcomes of interest without assigning treatments to the participants, whereas in experimental studies researchers assign treatments (usually randomly) to the participants.

Treatments for Depression in Bipolar Disorder (BD) Are Far Less