eq-5d eq-5d eq-5d is a standardised measure of health-related quality of life developed by the euroqol group to provide a simple, generic questionnaire for use in clinical and economic appraisal and population health surveys. eq-5d assesses health status in terms of five dimensions of health and is considered a ‘generic’ questionnaire because these dimensions are not specific to any one patient group or health condition. eq-5d can also be referred to as a patient-reported outcome (pro) measure, because patients can complete the questionnaire themselves to provide information about their current health status and how this changes over time. ‘eq-5d’ is not an abbreviation and is the correct term to use when referring to the instrument in general. eq-5d is widely used around the world in clinical trials and real-world clinical settings, population studies, and health economic evaluations. by mid-2020, the number of eq-5d studies registered with the euroqol group totalled over 39,000. these comprised over 80 clinical areas and related to surgical procedures, hospital waiting lists, physiotherapy, general practice and primary care, and rehabilitation. the number of annual requests to use eq-5d is approximately 5000, and eq-5d data have been reported in over 8000 peer-reviewed papers over the past 30 years. eq-5d can be used for a variety of purposes. in clinical trials and routine clinical settings, eq-5d can be used (i) to provide a profile of patient health on the day of questionnaire completion; (ii) to monitor the health status of patient groups at particular times, e.g. at referral, admission, discharge, and follow-up; and (iii) to measure changes in health status over time in individual patients and in cohorts of patients, such as before and after health interventions and treatments. in population studies, eq-5d can be used to assess population health status at local and national levels and to follow population health status over time. in medical decision-making, eq-5d can be used (i) to measure the impacts and outcomes of healthcare services; (ii) to provide relevant information for the economic evaluation of health programmes and policies; and (iii) to assist in providing evidence about effectiveness in processes where drugs or procedures require approval. eq-5d is recommended by many health technology assessment (hta) bodies internationally as a key component of cost-utility analyses. eq-5d was developed by the euroqol group, and its distribution and licensing are managed by the euroqol research foundation. the euroqol website provides detailed information and the latest developments about eq-5d including guidance for users, a list of available language versions and value sets by country/region, population norms, and key eq-5d references. it also explains how to obtain the questionnaire. those wishing to use eq-5d must first register their study or trial via the website, using the page ‘how to obtain eq-5d’, which has more detailed information about registering, including an animated video. eq-5d is provided without charging a license fee to non-commercial organisations after they have registered (approximately 95% of users), while commercial users are charged a fee. registering a study does not obligate the purchase of an eq-5d licence, but it enables the euroqol research foundation to provide further information relevant to the type of study proposed, including terms and conditions (and licence fees if applicable). development the euroqol group first met in 1987 with the goal of identifying a set of standardised questions that could be used to collect data on how people's lives were affected by illness and by health interventions. what was originally termed ‘the euroqol instrument’ was developed by 1990 and contained questions on five aspects (or ‘dimensions’) of health, with three levels of severity in each dimension. it was constructed simultaneously in five languages: dutch, finnish, norwegian, swedish, and english (which was to function as the source, or reference, language). the questionnaire was renamed ‘eq-5d’ in 1995 and now comprises a family of questionnaires: the three-level eq-5d-3l, the five-level eq-5d-5l, and the youth version eq-5d-y. eq-5d was designed as a self-completed questionnaire to fulfil two functions: (i) to provide a descriptive profile of current health status; and (ii) to provide a way of assigning a single numerical value to each of the possible health states described by the descriptive system, for use in economic evaluations of health care. the requirements for its design were that (i) the dimensions should be relevant to both patients and members of the general population; (ii) the descriptive system should be simple – with as few dimensions as possible, and as few levels as possible within each dimension; (iii) it should be short and easily self-completed in a range of settings, and simple enough not to require detailed instructions; and (iv) it should be reliable, valid, and able to identify changes in health status related to illness and health interventions. components the eq-5d essentially consists of two pages: the eq-5d descriptive system (page 2 of the questionnaire) and the eq-5d visual analogue scale (eq vas) (page 3 of the questionnaire) (video: explaining the eq-5d in about two and half minutes). as noted above, ‘eq-5d’ is not an abbreviation and is the correct term to use when referring to the instrument. sample versions in uk english can be viewed at https://euroqol.org/eq-5d-instruments/sample-demo/. descriptive systems the eq-5d descriptive system comprises five dimensions: mobility, self-care, usual activities, pain and discomfort, and anxiety and depression. the number of levels in these dimensions differ in the eq-5d-3l (three levels) and the eq-5d-5l (five levels). the eq-5d-y has the same five dimensions, but they are worded more appropriately for young people. eq-5d-3l in eq-5d-3l, the five dimensions each have three response levels of severity. the mobility dimension ranges from ‘i have no problems walking about’ to ‘i am confined to bed’. the self-care dimension ranges from ‘i have no problems with self-care’ to ‘i am unable to wash or dress myself’. the usual activities dimension concerns work, study, housework, family, or leisure activities and ranges from ‘i have no problems doing my usual activities’ to ‘i am unable to do my usual activities’. the pain/discomfort dimension ranges from ‘i have no pain or discomfort’ to ‘i have extreme pain or discomfort’. the anxiety/depression dimension ranges from ‘i am not anxious or depressed’ to ‘i am extremely anxious or depressed’. respondents are asked to choose the statement in each dimension that best describes their health status on the day they are surveyed. their responses are coded as a number (1, 2, or 3) that corresponds to the respective level of severity: 1 indicates no problems, 2 some problems, and 3 extreme problems. in this way, a person's health state profile can be defined by a 5-digit number, ranging from 11111 (having no problems in any of the dimensions) to 33333 (having extreme problems in all the dimensions). the health state 12321 would indicate a person having no problems with mobility, having some problems with self-care, being unable to perform their usual activities, having some pain or discomfort, and not being anxious or depressed. in total, the eq-5d-3l describes 243 (=3⁵) potential health states. eq-5d-5l eq-5d-5l was introduced in 2009 with the aim of enhancing instrument sensitivity and providing respondents with the opportunity to provide a more detailed and accurate picture of their health. the eq-5d-5l descriptive system uses the same five dimensions as the eq-5d-3l but has two extra levels of severity in each dimension. the five levels in each dimension are worded as (1) ‘not /no problems’, (2) ‘slight problems’, (3) ‘moderate problems’, (4) ‘severe problems’, and (5) ‘unable to’ (mobility, self-care, usual activities), ‘extreme’ (pain/depression), or ‘extremely’ (anxiety/depression). a few changes in the wording of some levels were also made. for example, in the mobility dimension, the 3l term ‘confined to bed’ has been replaced with ‘unable to walk about’ in the 5l; and the first level of self-care in the 5l now refers to washing and dressing, to be consistent with the other levels. because of the additional levels in eq-5d-5l, the descriptive system describes 3125 (=5⁵) potential health states. eq-5d-y the eq-5d version (eq-5d-y) was introduced by the euroqol group in 2009 as a more suitable questionnaire for children and adolescents. it is based on the eq-5d-3l, but the wording has been modified to be more easily understood and relevant for younger people. the dimensions are: mobility (walking about); looking after myself; doing usual activities (e.g., going to school, hobbies, sports, playing, doing things with family and friends); having pain or discomfort; and feeling worried, sad, or unhappy. the levels for the first four dimensions are: ‘none/no problems’, ‘some (problems)’, and ‘a lot (of problems)’. the levels in the feeling worried, sad, or unhappy dimension are: ‘not’, ‘a bit’, and ‘very’. eq-5d-y is recommended for use with 8–11-year-olds and for 12–15-year-olds (although the adult version may be appropriate in the older age group, depending on study design; see table 1. for children aged 4–7 years, a proxy version should be used – i.e. a version of the questionnaire that is suitable for completion by a third party (e.g. a parent, caregiver, or health professional) on the child's behalf. table 1: recommended age range of users of the eq-5d-y version age range recommendation 0–3 years no eq-5d-y version is available for this age range 4–7 years for children aged 4–7, a proxy version should be used no self-reported eq-5d-y is available for this age range at present. 8–11 years use eq-5d-y the eq-5d-y is more understandable for children in this age range than an adult version of the eq-5d 12–15 years both the eq-5d-y and adult eq-5d versions can be used an overlapping area. generally, eq-5d-y is recommended. depending on the study design, however, it might be appropriate to use one of the eq-5d adult versions. for example, if a study includes both adult respondents and respondents between the ages of 12 and 15, the study team might prefer to use just one version of eq-5d across the whole study population. 16 years and over use an adult version (eq-5d-3l or eq-5d-5l) a possible exception would be a study that only includes children up to age 18. in this case, eq-5d-y would be recommended across the full age range, to avoid using two different versions of eq-5d. eq vas the second part of the questionnaire in all three versions of eq-5d comprises a standard vertical 20-cm vas that is calibrated from ‘the worst health you can imagine’ (scored 0) at its base to ‘the best health you can imagine’ (scored 100) at its apex. respondents are asked to ‘mark an x on the scale to indicate how your health is today’ and to write the number in an adjoining box. this procedure makes it possible for respondents to provide a rating of their overall health on the day they complete the questionnaire. the vas can also be used to assess changes in a patient's perception of their own health over time. for example, a patient may rate their current health as 50 on the scale, but after a medical intervention the respondent's rating may be 85, reflecting a substantial improvement in health status. when a group of patients completes the eq-5d questionnaire before and after treatment, the change in self-rated health can be recorded from the vas data. eq-5d versions modes of administration eq-5d is available in different formats depending on the mode of administration. the 3l, 5l, and y versions can be self-completed on paper or by telephone or digitally, e.g., laptop/desktop, tablet, redcap, interactive voice response (ivr), and smartphone/personal digital assistant (pda). the eq-5d can be hosted on local servers or on alternatives such as redcap, limesurvey, castor edc, or qualtrics platforms. if people are unable to complete the eq-5d themselves for any reason, e.g. due to ill-health or literacy problems, interviewer-administered versions are available for use in telephone, online, or face-to-face interviews. it is sometimes appropriate to ask a caregiver (or proxy) to answer on behalf of people who cannot complete the questionnaire themselves (e.g. because they are too young, too ill, or have severe mental health problems or intellectual disability). the eq-5d has two proxy versions: proxy version 1 asks the proxy to provide their own rating of the other person's health, while proxy version 2 asks the proxy how they think the person being evaluated would describe his/her own health if they were able to complete the questionnaire. translations eq-5d is available in more