Cochrane Early Career Professionals lecture series: case-control studies

Dr. Denner explains how to design case-control studies, select appropriate control groups, calculate odds ratios, and recognize retrospective biases.

In this session, Dr. Denner (Senior Internal Medicine Resident at the University of São Paulo, Brasil) guides us through Case-Control Studies—explaining how to evaluate rare diseases, select appropriate control groups, calculate and interpret Odds Ratios (OR), and recognize major retrospective biases. This series is a project led by the Cochrane Early Career Professionals Network, designed to build core skills in evidence-based healthcare for medical students, early-career researchers, and healthcare professionals worldwide. In this session, you will learn: • How a case-control study is designed and conducted • Why case-control designs are ideal for rare outcomes or long latency periods • Key rules for case definition and control selection • Understanding the optimal control-to-case ratio • Major retrospective biases: selection, information, recall, and interviewer bias. • Why odds ratios are used instead of relative risk • Key takeaways ⏱️ Timestamps: 00:00 - Introduction & overview of the Cochrane Early Career Professionals Network 03:39 - Speaker introduction: Dr. Denner 04:40 - Clinical vignette: investigating risk factors for rare sarcomas 05:43 - Why cohort studies fail for rare diseases 07:00 - Fundamentals of the case-control design 08:23 - Precise case definition 09:34 - Selecting appropriate controls & control sources 11:47 - Recruitment ratios (cases to controls) 12:39 - Pros & cons of case-control studies 14:03 - Critical biases: selection, information, recall, & interviewer bias 17:40 - Why we use odds ratios instead of relative risk 20:00 - Calculating odds ratios & the rare disease assumption 22:05 - Interpreting odds ratios & causality vs. association 24:01 - Summary