Thoracic surgery is a rapidly evolving field, in continuous need of high quality clinical evidence. Case control studies are a type of observational study in which two existing groups differing in outcome are identified and compared on the basis of some supposed causal attribute. Case-control studies are often used to identify factors that may/may not contribute to a medical condition by comparing subjects who have that condition/disease (cases) with patients who do not have the condition/disease but are otherwise similar (controls). They require fewer resources but provide less evidence than a randomized controlled trial. As analytical observational studies, control studies are analytical observational studies that represent level II-2 clinical evidence (1).