Examining the empirical evidence for IDEAL 2b studies: the effects of preceding prospective collaborative cohort studies on the quality and impact of subsequent randomized controlled trials of surgical innovations – protocol for a systematic review and case–control analysis

Randomized controlled trials (RCTs) in surgery face methodological challenges, which often result in low quality or failed trials. The Idea, Development, Exploration, Assessment and Long-term (IDEAL) framework proposes preliminary prospective collaborative cohort studies with specific properties (IDEAL 2b studies) to increase the quality and feasibility of surgical RCTs. Little empirical evidence exists for this proposition, and specifically designed 2b studies are currently uncommon. Prospective collaborative cohort studies are, however, relatively common, and might provide similar benefits. We will, therefore, assess the association between prior ‘IDEAL 2b-like’ cohort studies and the quality and impact of surgical RCTs. We propose a systematic review using two parallel case–control analyses, with surgical RCTs as subjects and study quality and journal impact factor (IF) as the outcomes of interest. We will search for surgical RCTs published between 2015 and 2019 and and prior prospective collaborative cohort studies authored by any of the RCT investigators. RCTs will be categorized into cases or controls by (1) journal (IF ≥or <5) and (2) study quality (PEDro score ≥or < 7). The case/control OR of exposure to a prior ‘2b like’ study will be calculated independently for quality and impact. Cases will be matched 1: 1 with controls by year of publication, and confounding by peer-reviewed funding, author academic affiliation and trial protocol registration will be examined using multiple logistic regression analysis. This study will examine whether preparatory IDEAL 2b-like studies are associated with higher quality and impact of subsequent RCTs.