In 2005, a task force was formed within the so-called EuroQol Group to further develop the EQ-5D-3L and thereby improve it. The specific goal was to increase sensitivity and reduce ceiling effects. These efforts eventually led to the development of the EQ-5D-5L.1
The task force decided to keep the number of 5 dimensions and to increase the number of possible answers from 3 to 5 levels. Evidence from 25 years of use confirmed the validity of the 5 chosen dimensions.1-6
The EQ-5D-5L, like its predecessor, is a Patient Reported Outcome (PRO) instrument that can generally assess the quality of life of patients, regardless of disease, via 6 questions. It also includes a vertical EQ visual analog scale (EQ VAS, 0-100 points) and a descriptive EQ-5D-5L system. The latter assesses the following 5 dimensions or subscales over 5 levels / response options.1
5 dimensions (1 item each)
As with the EQ-5D-3L, the descriptive EQ-5D-5L system defines so-called EQ5D Health States. A total of 3125 (=55) different health states can be recorded. Depending on the level, a number is assigned to each dimension resulting in a 5-digit number combination.
Example: A patient has no problems with mobility (level 1), slight problems with self-care (level 1), moderate problems with general activities (level 3), moderate pain (level 3) and is not anxious. His EQ5D Health State is accordingly 12331. A completely healthy patient would have a number of 11111.
This 5-digit number can be converted into a numerical value using a special algorithm that is not publicly available. This score is called the EQ-5D-5L Index and represents the patient’s state of health. The algorithm for calculating the EQ-5D-5L Index is based on country-specific values for the EQ-5D-3L. Through crosswalk studies with a collective of 3691 patients, an adequate link has been established between them.
For calculations, the links have been translated into mathematical functions. Thus EQ-5D-5L crosswalk value sets have been created, with which the EQ-5D Health States or their 5-digit numbers can be used to calculate the respective EQ-5D-5L index. An index value of 1 represents the best possible state of health, while an index value of <0 (variable) represents the worst possible state of health.
Whether the patient’s specific EQ VAS score plays a role in the calculation of his or her EQ-5D-5L index cannot be determined due to the non-public algorithm.
The EQ-VAS score is measured on a scale of 0-100 points depending on where the patient has set his marker. 0 points indicates the worst possible state of health, whereas 100 points indicates the best possible state of health.
The EQ-5D-5L is a validated and established questionnaire that can be implemented in clinical research and patient care without much effort due to its small size.7-14 EuroQol member studies have also shown that it has higher statistical reliability and sensitivity compared to EQ-5D-5L, while its ceiling effect is lower. Last but not least, it is able to differentiate between considerably more health states by its finer subdivision of response possibilities and is therefore even more significant.15-18
Although being lower than at the EQ-5D-3L, a ceiling-effect is still detectable.19
The use and evaluation of the EQ-5D-3L requires a license. The amount of the license fee depends on the study type, donor, cohort size and language.20
The EQ-5D-5L is a successful further development of the EQ-5D-3L, which has been validated many times and is still widely used today. Its strong significance, combined with its small size, provide ideal conditions for efficient use in clinical research and patient care.