Questions 1-4.Investigators are interested in identifying whether physical exercise improves the depressive symptom scores. Investigators allocated 120 depressed patients to either receive standard care alone, or standard care with adjunct exercise treatment for 12 weeks. Exercise treatment included one supervised and two at-home exercise sessions per week at moderate intensity. Health information, including depression scores, was assessed at enrollment, and after 12 weeks. Investigators found a strong association of exercise treatment with low depression symptom scores. They also found that depressed individuals who received exercise sessions were more likely to drop out of the study than others.

Q1. The study design and an appropriate measure of association:

Q2. A source of bias that may be present based on the information provided:

Q3. How this bias is classified:

Q4. What would be its likely effect on the measure of association: