2.1. Survey Design and Sampling Framework

We conducted a cross-sectional survey in non-institutionalized persons older than 18 years, selected from the Romanian population. The data collection occurred from November 2018 to November 2019. We selected study participants from both rural and urban areas, out of a total number of 3181 settlements. Settlements were randomized and stratified to ensure representativeness, using the Romanian electoral register as the sampling frame. A total of 32 settlements (primary sampling units) were selected. Within each settlement, households and individuals were selected using a random route sampling method and the next birthday rule (the person whose birthday was closest to the interview date was interviewed), respectively [37]. Respondents signed a written consent to take part in the research and were offered no incentives for their participation. Ten percent of respondents were contacted by phone to verify that all data collection procedures were implemented as intended.

The sample size needed for national representativeness was estimated at 1794 with a maximum error of ±3% for a confidence level of 95% and including a 10% nonresponse rate [38]. The sample size needed for an EQ-5D-3L valuation study is 300 people [16]. To meet the representativeness criteria and to allow implementation of a parallel EQ-5D-5L valuation study, the final sample size was set at 1794. This article only targets the results of the EQ-5D-3L.