 The development of SBRT for treatment of stage I NSCLC non-small cell lung cancer inspired the collaboration between thoracic surgery and radiation oncology and has prompted the investigators to work closely together to evaluate the relative role of SBRT and surgery. Comparative studies of these modalities have been limited in number and are often difficult to interpret due to variability in methodological issues. The productive collaboration has resulted in publication of several studies comparing SBRT and surgery utilizing propensity score based analyses to match patients from each group. However, matching on limited numbers of variables between patients ultimately selected for therapy based largely on their real or perceived comorbidity leads to significant reporting bias, and therefore methods to comprehensively assess comorbidity are necessary. 