2016-04-01

Addendum to article

Addendum to the article ”Crosswalk algorithms for the conversion of mean EQ-5D indices calculated with different value sets” published in ”Scandinavian Journal of Public Health” 2016.

Tool to convert between Swedish and UK EQ-5D index values (works both ways):

The EuroQol’s EQ-5D questionnaire is a frequently used tool for heath economic and health related quality of life studies, The EuroQol’s 3 level EQ-5D questionnaire exists in 141 different languages 1. It has 5 dimensions (mobility, self-care, usual activity, pain/discomfort and anxiety/depression) and three distinct levels (‘no problems’, ‘some problems’, and ‘extreme/unable to/confined to bed’) that can be weight together into a single index by applying a value set. The value sets denotes the losses in quality-adjusted life years for every that every deviance from the ‘no problems’ state.

The EuroQol’s EQ-5D questionnaire is available in 141 different languages, while the EuroQol Group enterprise (www.euroqol.org) lists only 13 different country specific value set and for one Europe. For long is Sweden (and many other countries) the IK TTO value set have been used, due to the lack of country specific value sets.

Such a value set was recently developed by Burstörm and colleagues 2 for Sweden. The present tool aims to help researchers to crosswalk aggregated EQ-5D index values form the UK TOO to the Swedish TTO scale, and inverse.

The value sets

The EQ-5D questionnaire comprises 5 dimensions of health with 3 possible levels. The possible combinations of the EQ-5D dimensions and levels can generate 243 different health profiles or health states. These health states can be summarized into a single utility index. In this formula, the used beta coefficients were the weights of the United Kingdom time-trade-off (UK TTO) value set 3 and the Swedish TTO value set 2. For the Swedish TTO value set the N3 term takes value 1 if any dimension is at level 3, 0 otherwise. The UK TTO value set has two such indicator functions, one that takes value 1 if at least one dimension is at level 2 or 3, 0 otherwise. The second indicator function takes value 1 if any dimension is at level 3, 0 otherwise. The possible values of the UK TTO EQ-5D index range between -0.594 and 1. Theoretically the Swedish TTO EQ-5D index ranges between 0 and 1. However in practice the lower bound is 0.3402, denoting rescaled TTO value the value that in average patients whom report 33333 have, and upper bound of 0.9694 denoting the average rescaled TTO value of patients who report 11111. Table 1 summarizes the values of the two value sets.

UK to Swedish TTO:

0.5922 + 0.3596 × UK TTO


Swedish to UK TTO:

-1.6468 + 2.7800 × Swedish TTO



Table 1. The UK and Swedish TTO value sets for EQ-5D.

  UK TTO Swedish TTO
Full health 1 0.9694
Mobility
  Level 2 -0.069 -0.0666
  Level 3 -0.314 -0.1247
Self-care
  Level 2 -0.104  
  Level 3 -0.214  
  Level 2 & 3   -0.0276
Usual activities
 Level 2 -0.036 -0.1012
 Level 3 -0.094 -0.1355
Pain/discomfort
 Level 2 -0.123 -0.0345
 Level 3 -0.386 -0.0904
Anxiety/depression
 Level 2 -0.071 -0.0552
 Level 3 -0.236 -0.2077
At least one 2 or 3 -0.081  
At least one 3 -0.269 -0.0433



Table 2. Characteristics of the UK TTO and Swedish TTO value set estimation methods.

  UK Sweden
Method TTO TTO
Values Hypothetical Experience-based
Sample size 2997 51,254
Statistics Generalized Least Squares Ordinary Least Squares
Anchored Full health (11111) to 1 and dead to 0 No
Rescaling t/10 for states rated better than dead
t/(10-t) for states rated worse than dead
t/10


TTO, time-trade-off
t, number of years spent in full health


References

  1. EuroQolGroup. EuroQol - a new facility for the measurement of health-related quality of life. Health Policy. 1990; 16: 199-208.
  2. Burström K, Sun S, Gerdtham U-G, et al. Swedish experience-based value sets for EQ-5D health states. Qual Life Res. 2013: 1-12.
  3. Dolan P. Modeling Valuations for EuroQol Health States. Medical Care. 1997; 35: 1095-108.