A good use of time? Providing evidence for how effort is invested in primary and secondary outcome data collection in trials

Data collection is a substantial part of trial workload for participants and staff alike. How these hours of work are spent is important because stakeholders are more interested in some outcomes than others. The ORINOCO study compared the time spent collecting primary outcome data to the time spent collecting secondary outcome data in a cohort of trials.

We searched PubMed for phase III trials indexed between 2015 and 2019. From these, we randomly selected 120 trials evaluating a therapeutic intervention plus an additional random selection of 20 trials evaluating a public health intervention. We also added eligible trials from a cohort of 189 trials in rheumatology that had used the same core outcome set.

We then obtained the time taken to collect primary and secondary outcomes in each trial. We used a hierarchy of methods that included data in trial reports, contacting the trial team and approaching individuals with experience of using the identified outcome measures. We calculated the primary to secondary data collection time ratio and notional data collection cost for each included trial.

We included 161 trials (120 phase III; 21 core outcome set; 20 public health), which together collected 230 primary and 688 secondary outcomes. Full primary and secondary timing data were obtained for 134 trials (100 phase III; 17 core outcome set; 17 public health). The median time spent on primaries was 56.1 h (range: 0.0–10,746.7, IQR: 226.89) and the median time spent on secondaries was 190.7 hours (range: 0.0–1,356,832.9, IQR: 617.6). The median primary to secondary data collection time ratio was 1.0:3.0 (i.e. for every minute spent on primary outcomes, 3.0 were spent on secondaries). The ratio varied by trial type: phase III trials were 1.0:3.1, core outcome set 1.0:3.4 and public health trials 1.0:2.2. The median notional overall data collection cost was £8015.73 (range: £52.90–£31,899,140.70, IQR: £20,096.64).

Depending on trial type, between two and three times as much time is spent collecting secondary outcome data than collecting primary outcome data. Trial teams should explicitly consider how long it will take to collect the data for an outcome and decide whether that time is worth it given importance of the outcome to the trial.