The contribution of observational studies to the knowledge of drug effectiveness in heart failure

Aims Randomized controlled trials (RCTs) are the golden standard for the assessment of drug efficacy. Little is known about the add-on value of observational studies in heart failure (HF). We aimed to assess the contribution of observational studies to actual knowledge regarding the effectiveness of angiotensin-converting enzyme inhibitors (ACEI), and β-blockers (BB) in HF. Methods Observational studies that assessed the effectiveness of ACEI and BB in HF were identified by searching Medline, Embase, Cochrane Database (1990–2005) and the bibliographies of published articles. Cohort, case–control and time-series analysis studies were considered for inclusion. Studies with