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. Do you have difficulty communicating? The WGSS uses a four-level scale (no difficulty, some difficulty, a lot of difficulty, or cannot do entirely) to capture individuals’ degree of functional difficulty in each of the six domains.

The WGSS has undergone extensive cognitive and field testing in multiple languages and locations (Madans, Loeb, & Altman, 2011, Miller 2016). It is an internationally tested and widely accepted tool (Groce and Mont 2017). The UN Statistical Commission and the UN’s Economic Commission for Europe’s Council of European Statistics recommended the WGSS for collection of disability information for the 2020 round of censuses.

These questions on functional difficulties are not without limitations. For instance, although tested in 14 countries (Miller 2016), an understanding of functional difficulties in the WGSS may be limited in a context with limited access to health care and may lead to underreporting (Schneider 2016). The WGSS covers only a few domains and may well under-identify people with psychological difficulties, a concern that may be alleviated to some extent in the WGSSEnhanced, which is the short set and four additional questions on anxiety and depression, and another two on upper body mobility.

# **_Other functional difficulty questions_**

Functional difficulty questions may be found in questions that are different from those in the WGSS and in other international questionnaires.

First, although the WG recommends that the WGSS be adopted as is, some data sets have included selected questions only, changed the answer scale or the wording of questions, and/or altered the introduction to the questions. There are thus data sets that have questions somewhat similar to the WGSS.

In addition, there are functional difficulty questions that are independent of the WGSS. Some internationally tested survey tools such as the Model Disability Survey (Cieza et al 2018) or WHO-DAS 2.0 (WHO 2020) and other recent tools (e.g. Trani et al., 2015, Eide et al 2006) do include functional difficulty questions. For instance, WHO-DAS 2.0 has questions on cognition, mobility, and self-care.

# **Activities of Daily Living**

Disability has been measured using difficulties in Activities of Daily Living (ADL). There are different types of ADLs, including basic and intermediate. Basic ADLs are fundamental for body functioning (e.g. walking a specific distance) and include self-care activities such as feeding oneself, going to the bathroom without help, and dressing without help, bathing, eating, walking, toileting, urination and defecation. Intermediate ADLs are more complex tasks such as shopping, housekeeping, food preparation, and managing money.

ADL questions were initially developed to capture the physical effects of aging, and, as such, in some surveys the questions are only administered to respondents above a certain age (e.g. 45 and above). Intermediate ADLs include role activities, such as caring for others, that can be broad 6