Randomized controlled trials (RCTs) are the traditional gold standard evidence for medical decision-making, including decisions regarding drug safety. However, protocols that limit enrollment eligibility introduce selection error that severely limits a RCT's applicability to a wide range of patients.  This is especially problematic for broad safety assessment where the trial protocol specifically excludes those at risk of adverse events.  Conversely, high quality observational data can be representative of entire populations, but freedom to choose treatment can bias estimators based on this data. However, observational data may be used to quantify the size of possible bias due to recruitment protocols.  We also propose an estimator of effect size that capitalizes on RCTs' strong internal validity and observational studies' strong external validity.