Discussion
We aimed to derive disability weights for 82 health states based on health state valuations of nationally representative samples from four European countries. The resulting disability weights ranged from 0.005 for mild impairment of distance vision and mild anaemia to 0.761 for intensive care unit admission. We found a logical order in disability weights for all health states with multiple severity levels—that is, mild health states had lower values compared with moderate and severe health states. This is indicative of high face validity. This logical ordering of health states with different severity levels was also observed in the GBD 2010 and EURO disability weights studies.10 13
Some of the health states included in this study were also included in the GBD 2010 and EURO disability weights studies.10 13 Comparison of disability weights of these health states showed a high correlation between these studies, particularly between the EURO disability weights measurement study and this study.13 However, the actual disability weights derived from this study were slightly lower compared with the GBD 2010 disability weights measurement study.10 Since the evaluated health state descriptions and valuation method used were the same, an explanation for this finding may lie in a difference in the health state preferences of this study population versus the GBD 2010 disability weights measurement study.10 In this study, the population consisted of individuals from the general population of four European countries, whereas the GBD 2010 disability weights measurement study was based on health state valuations of individuals from more than 175 (small) geographical areas.
Previous studies have indicated that contextual differences may play an important role in health state valuations using paired comparisons15 16; these contextual factors may have resulted in differences in health state valuations and, therefore in slightly different disability weight values for the same health states. In particular, disability weight values that were derived based on responses of a Japanese versus Chinese versus European sample varied.13–16 For instance, in disability weights measurement studies conducted in China and Japan, it was observed that disability weights assigned to mental health symptoms were lower compared with those conducted in Europe.13–16 It was also found that disability weights for severe alcohol use disorder were lower in Fujian (China) than in Japan.15 36 Our findings did not indicate large contextual differences among our study participants. We found a high correlation within country-specific coefficients as well as between country-specific and pooled coefficients. This suggests that health state valuations based on paired comparisons are consistent across the European countries. This also confirms the results observed in the EURO disability weights measurement study where similar high correlations were observed.13 It is also possible to use the disability weights from our study in non-European region countries, but it is important that researchers keep in mind that these findings reflect the health state preferences of European populations and that, ideally, disability weights for noise-related health states are derived for the population under study.
Furthermore, the test–retest reliability of the paired comparison task was slightly higher (same order: 0.78; reversed order: 0.73) compared with the EURO disability weights measurement study13 (same order: 0.75; reversed order: 0.73), with little differences in test–retest reliability among individuals with different educational levels. This indicates that the quality of the paired comparison data was high and consistent across the educational levels of the respondents. The findings underline that the paired comparison technique is suitable for health state valuations in the general population, due to the low cognitive burden of the task, and possibly, also to the brevity of and lay terminology used in the descriptions of the health states.
Our study focused on environmental noise-related disability weights, such as noise annoyance and sleep disturbance. We estimated disability weights for moderate and severe annoyance to be 0.006 and 0.011, respectively. The disability weight for severe annoyance is much lower than the one (0.02) previously proposed by the WHO Regional Office for Europe18 37 and similar to that (0.01) proposed by van Kamp et al.38 An explanation for the former is that different methods for deriving disability weights result in different disability weight values.12 Considerable variations have been identified in health preferences and thus, in disability weights derived from, for instance, patients versus members of the general public or medical experts versus members of the general public.39–42 In fact, medical experts have greater understanding of or experience with specific medical conditions, which may result in different values for the same disability weights. In addition, the DALY metric explicitly views health as a vital population-based asset that enables individuals to live a long and healthy life, thereby making the integration of health preferences from (diverse) members of the general public vital. Furthermore, in this study a more detailed disaggregation of noise annoyance was used (ie, moderate and severe annoyance), whereas only one health state (ie, high annoyance) was previously considered.18 37 Future studies can therefore quantify environmental-related DALYs at both lower and higher granularity levels of noise annoyance, if epidemiological data exist.
Another noteworthy observation pertains to the difference between the disability weight for high sleep disturbance (HSD) estimated based on expert judgments and used by WHO (0.07)18 37 and the one estimated in this study which derived based on preferences from general populations (0.010). Nevertheless, the ranking of annoyance and sleep disturbance was similar across studies, with lower disability weights assigned to annoyance compared with sleep disturbance. Furthermore, our results indicate that including information about the environmental source of the symptoms and functional limitations described in the health state description resulted in inconsequential differences in disability weights (ie, disability weight for sleep disturbance: 0.009; 0.006–0.014 95% UI and disability weight for sleep disturbance with source: 0.010; 0.006–0.015 95% UI). Hence, one can assume that the same applies to noise annoyance and that information about the environmental source of a particular health state is not taken into account by participants when evaluating health states. However, it is strongly recommended to investigate this in future environmental noise-related disability weights measurement studies. It should also be noted that, additional information on functional impairments or symptoms was taken into account, as results from the EURO disability weights measurement study showed.13 In the EURO disability weights measurement study, two distinct health state descriptions for several health states with slight differences in the wording of functional impairments, resulted in, sometimes stark, differences in disability weights.13 In our study, we only investigated the impact of including environmental noise as the source of sleep disturbance. It remains to be investigated whether or not other sources of sleep disturbance (eg, smell or light exposure) also impact the evaluation of health states by the respondents.
A limitation of our study lies in the use of a web-based survey for data collection, which can be costly due to length of time required to collect data. However, computer-assisted personal interviews would probably have resulted in higher data quality, and delivered the most representative results. In addition, internet users are generally younger compared with the general population and highly educated individuals, with the Netherlands and Sweden having among the highest percentage of individuals with above-average basic overall digital skills in Europe, and Italy and Hungary having among the lowest compared with the European Union average.43 We sought to mitigate the above limitations by using (existing) large internet panels with regard to age, gender and highest level of education. Another limitation of our study lies in the formulation of lay health state descriptions for noise annoyance and sleep disturbance. The scarcity of information on the definition of noise annoyance and sleep disturbance versus insomnia as well as the lack of qualitative studies limit the development of precise lay descriptions for such noise-related health states. We sought to mitigate the above limitation by seeking opinion from medical experts as well as from environmental noise experts. However, one can argue that these lay descriptions need to be further refined, for example, by considering the functional limitations and/or psychological implications linked to these outcomes.44 45 Additionally, the WHO Environmental Noise Guidelines for the European Region and other studies have focused on (source-specific) exposure–response functions for noise-related HSD.37 46–48 We estimated disability weight for sleep disturbance (ie, with and without environmental noise as the source) and not for %HSD. This should be taken into account when applying both the disability weight for sleep disturbance and exposure–response functions in environmental noise-related burden of disease studies. Notwithstanding the above limitations, the resulting European NOISE disability weights set is consistent, and can be used to estimate the environmental burden of disease attributable to noise-related health outcomes across Europe and beyond.