Objective: To quantify the bias associated with nonrandomized study (NRS) design attributes in literature comparing Transcatheter Aortic Valve Implantation (TAVI) vs. Surgical Aortic Valve Replacement (SAVR).
Methods: 1) Conducted meta-analysis; 2) Compared estimates of treatment effects (ETE) between study designs; 3) Identified associations between 41 NRS attributes and pooled ETE.
Results: We included 87 NRSs and 6 randomized controlled trials (RCTs). Lower quality studies underestimated the benefit for TAVI. Randomization in low quality RCTs and risk adjustments in NRSs did not always bring estimates closer to high quality RCT compared to NRSs without adjustment. NRSs that described lost to follow-up reported ETE significantly closer to high quality RCTs than NRSs that did not.
Conclusion: ETEs in NRSs are often biased compared to RCTs. Simply categorizing a study as an RCT or NRS fails to reflect the range of bias in each category. Factors related to follow-up may explain important bias.M.Sc
