1. Benson K, Hartz AJ. A comparison of observational studies and randomized, controlled trials. The New England Journal of Medicine. 2000;342:1878-1886. DOI: 10.1056/NEJM200006223422506
2. Murad MH, Asi N, Alsawas M, Alahdab F. New evidence pyramid. Evidence-Based Medicine. 2016;21:125-127. DOI: 10.1136/ebmed-2016-110401
3. Zeng X, Zhang Y, Kwong JS, Zhang C, Li S, Sun F, et al. The methodological quality assessment tools for preclinical and clinical studies, systematic review and meta-analysis, and clinical practice guideline: A systematic review. Journal of Evidence-Based Medicine. 2015;8:2-10. DOI: 10.1111/jebm.12141
4. Grimes DA, Schulz KF. Cohort studies: Marching towards outcomes. Lancet. 2002;359:341-345. DOI: 10.1016/S0140-6736(02)07500-1
5. Aschengrau A, Seage GR. Cohort studies. In: Aschengrau A, Seage GR, editors. Essentials of Epidemiology in Public Health. 3rd ed. Burlington, MA: Jones & Bartlett Learning; 2013. pp. 205-232