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Why and how do we research disabilities

This article explores how and why we research disabilities.

There are a number of important reasons why we should collect data on disability: One, for advocacy, so that we can promote the full inclusion of people with disabilities in their societies on an equal basis with others. Two, for programme planning, so that we know how many people with disabilities there are, and the contexts that they live in. We need to know this to plan programmes that adequately meet their needs. And three, because The Sustainable Development Goals (SDGs) describe the need for inclusive development that “Leaves no one behind”.

We must ensure that data on disability is included in all reporting on achievements towards the SDGs so that we can assess how far each goal is achieved for people with disabilities and ensure they are not left behind. In order to collect data on disability, we need to be able to measure it. The most common way to measure disability in research is to ask people to self-report about their functioning. Functioning refers to the body functions and activity components of the ICF (see Step 1.5) – whether the person can see, hear or walk, for example. Different functions are known as functional domains.

Asking people to self-report their functioning doesn’t mean asking people “do you have a disability”, which we know can be stigmatising in many contexts and is likely only to identify people with the most substantial functioning limitations.

Instead, this means asking people whether they experience difficulties in different functional domains, or in doing common activities. We will discuss the most common approaches below.

1. The Washington Group Tools

The Washington Group on Disability Statistics  is a United Nations City Group, that has developed a number of tools to measure disability.

The most commonly used of these is the Washington Group Short Set (WGSS). WGSS aims to identify the majority of people at risk of participation restrictions because of a health condition or impairment. It focuses on six basic functional domains: seeing, hearing, walking, cognition, communicating and self-care.

The Washington Group Short Set of Questions (WGSS):
1. Do you have difficulty seeing, even if wearing glasses?
2. Do you have difficulty hearing, even if using a hearing aid?
3. Do you have difficulty walking or climbing steps?
4. Do you have difficulty remembering or concentrating?
5. Do you have difficulty (with self-care such as) washing all over or dressing?
6. Using your usual (customary) language, do you have difficulty communicating, for example understanding or being understood?
Response options for all questions: No, no difficulty; yes, some difficulty; yes, a lot of difficulty; cannot do at all

The questions can be analysed in different ways but the most common approach is to consider anyone who reports “a lot of difficulty” or higher in any domain as having a disability.

The WGSS are widely used and recommended, including for SDG Indicator disaggregation. They are simple, quick, reproducible and easy to translate into different languages. They are suited for use in censuses or in large surveys where only a few questions can be included, and as they are used widely, results can be compared over time and between countries. They are non-stigmatizing, as they do not ask about disability directly.

However, the WGSS provides limited data on other components of disability, such as participation restrictions or impairments. It also excludes psychosocial functioning and mental health.

The Extended Set of Washington Group questions (WGExS) contains up to thirty five questions, and can be used in surveys where more time is available. They capture a more complete picture of disability. Additional domains include psychosocial functioning, pain, fatigue and upper body function, as well as more in-depth questions related to the basic domains of the WGSS (e.g. separately asking about near and distance vision). The Washington Group have also collaborated with UNICEF to develop an extended set of questions on functioning for children aged 2 to 17.

Finally, the Washington Group “Enhanced Short Set” (WGES) is a hybrid tool which includes the 6 questions of the Short Set, plus six additional questions related to upper body strength and mental health:

Additional Questions in Enhanced Short Set (WGES)
7. Do you have difficulty raising a two-litre bottle of water from waist to eye level?
8. Do you have difficulty using your hands and fingers, such as picking up small objects like a button or pencil, or opening or closing containers or bottles? Response Options: As above
9. How often do you feel worried, nervous or anxious? Response Options: Daily, Weekly, Monthly, A few Times a Year, Never
10. Thinking about the last time you felt worried, nervous or anxious, how would you describe the level of these feelings? Response Options: A little, A lot, Somewhere in between a little and a lot
11. How often do you feel depressed? Response Options: Daily, Weekly, Monthly, A few Times a Year, Never
12. Thinking about the last time you felt depressed, how would you describe the level of these feelings? Response Options: A little, A lot, Somewhere in between a little and a lot
Defining disability is the same as the WGSS, plus including anyone who responds “daily” and “a lot” to either of the psychosocial functioning questions.

2. The Model Disability Survey

The Model Disability Survey (MDS) provides another self-reported approach to measuring disability. The MDS is a comprehensive population based survey that provides detailed information on the lives of people with disabilities. It views disability as the outcome of interactions between a person with a health condition and various environmental factors.

The MDS considers disability as a continuum that ranges from low to high levels of severity and measures both what the person is capable of doing in their current environment (performance) and what they would be capable of doing in a fully inclusive and accessible environment (capacity). Disability is defined based on complex statistical analysis undertaken by WHO Geneva, completed after the data is collected, cleaned and sent by partner countries. Short and Full versions of the survey protocol are available.

3. Participation Focused Approaches

In Great Britain, the legal definition of disability in the Equality Act 2010 includes “negative effect on your ability to do normal daily activities”. Consequently, the Office of National Statistics (ONS) in Great Britain have developed the Equality Act Disability Definition (EADD) a two-question tool for measuring disability according to the Equality Act, that emphasises impact on participation restrictions directly.

1. Do you have any physical or mental health conditions or illnesses lasting or expected to last 12 months or more? Response Options: Yes, No
2. If yes, Does your condition or illness/do any of your conditions or illnesses reduce your ability to carry-out day-to-day activities? Response Options: Yes, a lot, Yes, a little, No
A person is considered to have a disability if they answer yes and yes a lot, respectively.

Great Britain Equality Act Disability Definition

In a small study in 2019, the ONS compared responses to the EADD and the WGES, and found that the prevalence of disability in a predominantly older British sample was approximately twice as high for the EADD than the WGES using standard WG cut offs. This may be in part because EADD does not specify whether the person should consider any assistive devices (e.g. glasses, hearing aids) or medication (e.g. for arthritis, anxiety) in their response. It may also be because the WGES does not include limitation related to pain, fatigue or breathlessness, which can be common in older adults and would be picked up in the EADD through their impact on participation.

A similar tool called the Global Activity Limitation Instrument (GALI), also focused on participation restriction, is used by EUROSTAT in the European Health Interview Surveys and other harmonised European data collection.

Further research on the utility of such tools in other settings, and comparability of outputs compared to the WGSS, would be valuable.

4. Assessment of impairments or health conditions

Impairments or health conditions are components of disability that can be measured directly using objective testing (e.g. measuring vision impairment using a visual acuity chart). These data are important for planning appropriate health and rehabilitative services amongst those who would benefit from these (e.g. provision of cataract surgery, hearing aids, mobility devices). This may be particularly needed in low resource settings where inadequate access to health care is closely related to disability.

However, it is important to recognise that impairment and health condition testing in isolation does not consider the effect on the individual’s level of functioning or participation. This type of assessment may also be more resource intensive to undertake than gathering self-reported information. More information about impairment screening is available in the See Also section.


There is a growing emphasis on measuring disability in order to 1) estimate the prevalence of disability, 2) identify the needs of people with disabilities, and 3) monitor the inclusion of people with disabilities.

There are different self-reported approaches to the measurement of disability, which have advantages and disadvantages. Using commonly used tools and definitions like the WGES, and where appropriate using a combined approach of both self-report and assessment of impairments is recommended.

Approach Pros Cons
WGSS Recommended for SDG Data disaggregation, Simple and quick, Internationally comparable Misses psychosocial functioning, Does not measure participation restrictions
WGES As above, and includes psychosocial functioning and upper body domains Does not measure participation restrictions
Model Disability Survey Comprehensive survey methodology, Provides detailed information Requires complex statistical analysis, Time consuming and resource intensive compared to alternatives
EADD or GALI Concise, Includes participation restrictions Does not give detail on functional domains, Does not specify whether limitation is with or without assistive devices or medication
Clinical Assessment Provides relevant data for health and rehabilitation service planning Need for clinical equipment or personnel may increase resource burden


  • Imagine that you were completing a research study to find out whether people with disabilities in Vanuatu had adequate access to WASH, what tool would you use?
  • Imagine, instead, that you wanted to plan services for people with hearing impairments so were completing a population-based survey – what tool would you use then?
© London School of Hygiene & Tropical Medicine 2020
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