Objectives: The objective was to investigate the role of duet extraction in reducing data errors in evidence synthesis for pharmaceutical and non-pharmaceutical interventions. Design: Randomized controlled trial. Setting: University teaching center and hospital evidence-based medicine center. Participants: Eligible 100 participants were 2nd year or above post-graduate students (e.g., masters, doctoral program), who were randomly (1:1) assigned for data extraction tasks of either 10 RCTs of pharmaceutical interventions or 10 of non-pharmaceutical interventions, followed by a cross-over pattern and a further double-checking process. Intervention: The intervention of this trial was double-checking process for data extraction. Primary and secondary outcome measures: The primary outcome was the error rates for RCTs in the pharmaceutical versus non-pharmaceutical intervention group, in terms of both study level and cell level (2 by 2 table). The secondary outcome was the absolute difference in the error rates before and after the double-checking process for both the pharmaceutical and non-pharmaceutical intervention groups, again, in terms of both study level and cell level (2 by 2 table). Results: The error rates in RCTs of pharmaceutical and non-pharmaceutical groups were 64.65% and 59.90%, with an absolute difference of 4.75% and an odds ratio (OR) of 1.29 (95%CI: 1.06 to 1.57, P = 0.01) when measured at the study level. After double-checking, the error rates decreased to 44.88% and 39.54%, and the difference between the two groups remained at 5.34%, with the OR of 1.27 (95%CI: 1.1 to 1.46; P < 0.01). Similar results were observed when measured at the cell level. Conclusion: Double-checking reduced data extraction errors, but the error rate still remained high after the process. Further evidence synthesis research may consider to use triple data extraction to minimize potential errors. Trial registration number: Chinese Clinical Trial Registry Center (Identifier: ChiCTR2200062206)
