Commentary

Although large randomized clinical trials remain thefoundation for informing evidence-based prescrib-ing, vast data sources can provide insight into com-plex questions that arise in clinical decision-making. Using tens of thousands to millions of patients, registries and ad-ministrative databases now serve as the “living textbooks” envisioned more than 40 years ago.1 Common clinical ques-tions can now be readily addressed because of the marked advances in clinical data informatics and the application of information technology to clinical care. As an example of this wealth of data, in this issue of CMAJ, Pilote and col-leagues2 use administrative databases of hospital discharges and prescription claims to study the comparative effective-ness of angiotensin-converting-enzyme (ACE) inhibitors in the treatment of congestive heart failure. The value of renin–angiotensin–aldosterone inhibition in reducing mortality and morbidity among patients wit