1. A study is planned to assess the effects of a new drug designed to improve survival among patients with leukemia. The investigators believe that many factors affect survival among this patient group, including age, gender, nutritional status, functional status, and the presence of other diseases. The investigators wish to control for the potential confounding factors while evaluating the effects of the new drug. Which of the following is the most appropriate study designed for this purpose?

1. Case series
2. Case cohort study
3. Case-control study
4. Cohort study
5. Randomized controlled trial