EQ -5D scale has three versions: EQ -5D-5L, EQ -5D-3L and EQ-5D-Y. EQ -5D series scale aims to describe and evaluate the health status of patients in various disease fields. This series of scales has been widely used in clinical trials and population studies, and has been proved to have good reliability, validity and sensitivity in many disease fields and populations.
EQ -5D mainly consists of two parts: EQ -5D description system and EQ -5D visual simulation scale (VAS).
In the description part, the health status will be described from five dimensions: mobility, self-care, daily activities, pain/discomfort and anxiety/depression. The questionnaire asked respondents to choose the most appropriate option in each dimension according to their health status.
In the evaluation part, the respondents used the Visual Simulation Scale (EQ-VAS) to evaluate their overall health. EQ-VAS recorded the respondents' self-rated health status on the vertical scale. The scale is 0- 100, where 0 means "the worst health condition you imagine" and 100 means "the best health condition you imagine". Respondents' self-evaluation information can be used as a quantitative indicator of health results.
Let's introduce the specific system EQ-5D. When EQ -5D was first developed, three levels were used to describe health status:
For example, the three levels of the mobility dimension are expressed as:
Usually, we use the numbers 1, 2 and 3 to code these levels. 1 means there is no difficulty, 2 means there is some difficulty, and 3 means it is extremely difficult. In this case, a person's health can be defined by five numbers. The range is from1111(all dimensions have no problems) to 33333 (all dimensions have extreme problems). 1232 1 indicates that there is no problem with activity and anxiety/depression, but there are slight problems with self-care and pain/discomfort, and there are extreme problems with daily activities. According to the permutation and combination, EQ -5D-3L*** has 243(3 5) different health states.
With the extensive application of EQ -5D-3L scale, the limitations of 3L system are also exposed. For schizophrenia, alcohol dependence, hearing impairment and other diseases, 3L is not sensitive to the changes of middle and small health level, and has a weak response to the detection of clinical changes. In order to improve this limitation of 3L, the European Quality of Life Association has developed a new version of EQ -5D(EQ-5D-5L). In this new version, the options of each dimension are expanded from 3 levels to 5 levels:
Usually these levels are coded with the numbers 1, 2, 3, 4 and 5. 1 indicates no difficulty, 2 indicates some difficulty, 3 indicates moderate difficulty, 4 indicates serious difficulty, and 5 indicates no/very serious difficulty.
The validity and reliability of EQ 5D have been widely evaluated in different language versions and various health conditions, including cancer, type 2 diabetes, chronic obstructive pulmonary disease, asthma and cardiovascular diseases. Compared with 3L system, 5L system has faster response speed, better effectiveness and reliability.
Through the health description system of EQ-5D scale, a five-digit health status can be generated, which can be intuitively reflected in five health dimensions, such as 2 1232. Such health status can be converted into a single general number (utility index value) to reflect the health status according to the characteristics of the general population in a certain country/region.
The utility index of EQ-5D is calculated by a formula, which gives a value (weight) to each level of each health dimension of EQ-5D. The utility index can be obtained from 1 minus the corresponding weight of health status in each dimension, where 1 is the health utility value of complete health status11. I take the British EQ-5D-3L version as an example:
Let's look directly at the left part of the table without looking at a long list of formulas. For the 5-dimensional Level 2 and Level 3 answers, the corresponding weights are given in the table. The reason why 1 grade is not displayed here is because the weight of 1 grade is 0. In addition to the five dimensions, there are two kinds of situations with weight: there is at least one second or third level (at least one second or third level); Level 3 occurs at least once (at least one 3). In this way, the health status utility index value 2 1232 of EQ-5D-3L in the UK is equal to:
The weight values of EQ-5D in each dimension and grade are obtained from the study of standardized utility index valuation, which is generally carried out in a representative population sample of a country or region. This can ensure that the obtained index value represents the characteristics of the general population in society. From this website, you can find the valuation of utility index in different regions, https://euroqol.org/eq-5d-instruments/eq-5d-5l-about/evaluation-standard-value-sets/.
The above is the introduction of EQ -5D scale. If you have any questions, please feel free to give feedback in the comments section!