A pilot phase may increase the cost of valuation studies and is time consuming. It is currently unknown whether an extensive pilot phase has a meaningful impact on the performance of the interviewers and whether it may help minimize interviewer effects in EQ-5D-5L valuation studies.

This study highlighted the benefits of an extensive pilot phase on data quality and interviewer performance in terms of improvement in the face validity and reduction of prediction errors in the cTTO data during the whole data collection process and especially during the pilot phase.

A pilot phase may have substantial benefits for data collection of EQ-VT studies where it can help reveal issues and exclude poorly performing interviewers and might prove more beneficial in EQ-5D-5L valuation studies where protocol compliance issues and interviewer effects exist.