Norwegian population norms for the EQ-5D-5L: results from a general population survey

Age and sex-specific response rates to existing Norwegian postal surveys, including those designed to give population norms [11, 12, 27‐29], were assessed and determined the necessary sample size to give a similar number of respondents, and estimates of equal precision, per age and sex group. The National Registry of the Norwegian Tax Administration (Folkeregisteret) was used to select a random group of 12,790 adults aged 18 years and over, who in December 2019, were sent a postal questionnaire and reply-paid envelope addressed to the Norwegian Institute of Public Health. The accompanying letter explained the purpose of the study, that by responding to the questionnaire they gave their informed consent, and that those returning a completed questionnaire would be included in a lottery of ten prizes each to the value of NOK 10,000 (1000 Euro).

The EQ-5D-5L was translated into the Norwegian language in accordance with EuroQol translation procedures including forward backwards translation, cognitive debriefing, and quality control [30]. Used alongside the EQ-5D, the EQ VAS is a 20 cm vertical visual analog scale assessing “your own health today” on a scale of 0 to 100 corresponding to the worst and best imaginable health. Responses to the five items representing EQ-5D-5L health states are identified by a five-digit number (for example, 11232), each of which corresponds to the response category reported for successive dimensions, beginning with mobility. Each state has a value attached, which are based on national value sets, typically derived from general population studies, and used in the calculation of QALYs. In the absence of a scoring algorithm for Norway, the Norwegian Medicines Agency recommends [8] use of the UK EQ-5D-3L value set [9] mapped to the EQ-5D-5L descriptions of health [10], a “crosswalk value set”. This crosswalk value set was used for the Norwegian EQ-5D-3L population norms [11] and is available to the system of national quality [31, 32]. The questionnaire also included questions relating to age, gender, and education level.

The Regional Committee for Medical and Research Ethics stated that the study did not require their approval. The Data Protection Impact Assessment was approved by the Norwegian Institute of Public Health on the 16th October 2019.

Presentation of norms including descriptive statistics, follow existing EQ-5D-5L studies and include EQ-5D-5L dimension, index, and EQ VAS scores for the entire sample and by seven age groups, sex and education level [2, 14‐26]. The latter is less widely reported but has a consistent role in explaining lower EQ-5D scores [13]. The most widely reported health states are shown for EQ-5D-5L states with 0.5% or more responses. The data were weighted according to age, gender, and education level to improve representativeness of the Norwegian general population using data from Statistics Norway for 1 October, 2019. The latter were used to compute frequencies that adjust for over- or underrepresentation in relation to these characteristics.

Statistical analyses were performed in R version 4.0.4 [33].

Of the 12,790 questionnaires mailed, 426 were returned by the Post Office for being wrongly addressed, and one person had died. Of the remainder, 3200 (25.9%) returned a questionnaire that was at least partly completed. The results that follow are based on the 3120 (24.4%) respondents who completed the EQ-5D-5L dimensions and background questions. There were 73 fewer usable responses to the EQ VAS. The mean age (SD) was 50.9 (21.7) and ages ranged from 18 to 97 years (Table 1). There were approximately 10% more female respondents than male, and 239 to 691 respondents across seven age groups; the lowest number of respondents was for 80 years and above and the highest was for those 18–29 years of age. Respondents to the five education levels ranged from 282 to 862 for below secondary school to postgraduate higher education. Survey respondents are also over-represented for the youngest and oldest age groups, and highest education level. The final two columns of Table 1 show the number of respondents across these categories after weighting was applied.

Table 2 shows that almost one-third of respondents reported no problems on any of the five EQ-5D-5L dimensions, and 23% reported slight problems in relation to self-care. Twenty health states had frequencies of 0.5% and above, accounting for 84.3% of respondents. Of the possible 3125 EQ-5D-5L health states, 277 (8.9%) were reported.

The remainder of the results relate to the weighted data. The distributions of the EQ-5D-5L item responses for the seven age groups are shown in Table 3 and separately for females and males in Tables 4 and 5, respectively. Irrespective of age and sex, the great majority (76–93%) reported no problems with mobility, self-care, and usual activities. Two exceptions are mobility and usual activities for those aged 80 years and over, where approximately 50% of females and 60% of males reported no problems (Tables 4 and 5). The great majority (83%) reported none or slight pain/discomfort. For anxiety/depression the majority (65%) reported no problems, which is more apparent for older age groups. Apart from anxiety/depression, the proportion reporting no problems decreases with age (Tables 3, 4 and 5).

Responses to the two categories of severe or extreme problems ranged from 0.7 to 6.0% for the self-care and pain/discomfort dimensions, respectively (Table 3). Responses to the two categories of severe or extreme problems for the mobility and self-care dimensions, came mostly from the two oldest age groups. Severe and extreme problems for usual activities, pain/discomfort, and anxiety/depression were more evenly distributed across age groups with two exceptions; the age group 30–39 years, which had among the highest levels of health for four dimensions, and the youngest age group, which had highest reported levels of anxiety/depression.

The EQ-5D index and EQ VAS scores are shown in Table 6. Compared to males, females have slightly lower scores for the EQ-5D-5L index and similar scores for the EQ VAS. For all respondents, the index and EQ VAS scores follow a similar pattern across the seven age groups, with slightly higher scores for the age group 30–39 years compared to the youngest age group. The scores fall slightly for the next age group 40–49 years, increase for the age groups 50–59 and 60–69, and decrease in the oldest age groups. These fluctuations are slightly higher for the EQ-5D index scores in males compared to females. Both scores show a slightly different pattern for females and males. Compared to the EQ-5D index scores for the age group 40–49 years, the female age group 50–59 years has an increase, while the same male group has a decrease in scores. This pattern is reversed for the age group 60–69 years. Compared to the EQ VAS scores for the age group 19–29 years, the female age group 30–39 years has a decrease, while the same male age group has an increase in scores.

Both scores show a linear trend toward higher levels of health with the four levels of education from below upper secondary school level to postgraduate (Table 6). The differences between levels is very similar for the EQ-5D-5L and EQ VAS. The largest differences are for the first two levels of below and upper secondary school education. For both scores this difference is larger than that for the three remaining levels of education combined.

There is currently no Norwegian value set or scoring algorithm for the EQ-5D-5L. Norwegian data were being collected for this purpose [5], but was postponed because of the COVID-19 pandemic. Other countries have faced similar issues in the reporting of population norms [14, 26]. Norms for the EQ-5D index scores were based on the UK value set with a mapping algorithm, which follows current recommendations [8]. When a Norwegian value set becomes available, EQ-5D index norms will be updated accordingly, and users informed.

Electronic data collection, including internet administration, is increasingly used for collecting PROMs data, and this additional mode of administration would have strengthened the study. Instrument scores and measurement properties are generally comparable for electronic and pen and paper administration, but response rates tend to be lower, and respondents less representative for the former [36‐38]. EQ-5D data from internet panels have been shown to give systematically different respondents and norms to those from pen and paper administration [2]. Response rates to Norwegian surveys that include PROMs and related instruments including those assessing patient experiences, give lower response rates for internet compared to postal surveys and particularly for older age groups [11, 39, 40]. Norwegian norm data for the earlier version of the EQ-5D with three levels were collected in 2010 by postal and electronic means, and while the authors concluded that methodological considerations limited the comparison of the two response rates, there were just 57 respondents over 71 years of age in the electronic survey compared to 175 in the postal survey [11]. National surveys of patient experiences of health services quality in Norway span two decades, and while there has been a steady increase in both the use and response rates to internet surveys, response rates to the postal component continue to be highest [39, 40].