Frequency of receiving requested data for a systematic review and associated factors: A cross-sectional study

This study aimed to assess the frequency of receiving requested data for a systematic review and associated factors. We contacted the authors of studies in need of additional data via e-mail. The primary outcome was the success in receiving the requested data according to the time until receipt. We estimated the hazard ratio (HR) and 95% confidence interval (CI) for success in each variable compared to the reference category, with weighted Cox proportional hazards models using Stata (version 14.2). Out of 164 studies contacted, 110 replied (67.1%), and 51 sent requested data (31.1%). Median time to receive a response or withdraw contact was 36.0 days (interquartile range: 17.5, 142.5). Higher success ratio was observed in studies published as scientific papers (HR = 3.01, 95% CI = [1.18, 7.70]), in more than one publication (HR = 2.00, 95% CI = [1.14, 3.51]), and contacted by personal e-mail (HR = 2.85, 95% CI = [1.34, 6.07]). Three or more contact attempts led to lower success ratio (HR = 0.19, 95% CI = [0.11, 0.35]) than one or two. Requesting data for a systematic review was time-consuming and effective in three out of ten studies. Fewer contacts were more successful than insisting.