functional difficulties (e.g. difficulty seeing), activity restrictions (e.g. difficulty feeding oneself) and participation restrictions (e.g. restricted in socializing). This paper considers disability as an interactional and biopsychosocial phenomenon, consistent with the ICF and other interactional models (Goodley 2018, Mitra 2018).

Besides varying underlying measurement objectives and conceptual definitions, there are different ways to collect disability data. These are “self-perceived and observed” data (Murray and Chen 1992). Self-perceived measures give an individual’s own perception of limitations, while observed measures rely on an external party’s assessment. Both types of measures provide complementary and valuable information (Murray and Chen 1992). There is typically no observed data in surveys and censuses in low- and middle-income countries. Thus, self-reported measures are used in this study and are therefore the focus of this paper.

# **3. Disability questions in household surveys and censuses**

As can be anticipated, there are different ways to measure disability through self-reports (Mitra 2018; Palmer and Harley 2012). We describe below the different types of questions that have been commonly used in surveys and censuses: functional difficulties, activities of daily living, broad activity limitations, general disability/impairment questions and other questions.

# **Functional difficulties**

Functional difficulties refer to difficulties experienced with particular bodily functions such as seeing and hearing. The term is used to also include basic activities such as walking and daily activities such as feeding oneself. The United Nations Statistical Commission (United Nations 2015, 2017) adopted revised guidelines for the collection of disability data in national censuses. "It is suggested that only those domains that have satisfied a set of selection criteria be eligible for inclusion in a short set of questions recommended for use in censuses. Criteria for inclusion include cross-population or cross-cultural comparability, suitability for self-reporting and space on the census form. Other suggested criteria include the importance of the domain in terms of public health problems” (United Nations 2017). The Commission recommends that the following four functional domains be considered essential in determining disability status in a way that can be reasonably measured using a census and that would be appropriate for international comparison: (a) Walking; (b) Seeing; (c) Hearing; (d) Cognition. It also notes that two other domains, self-care and communication, have been identified for inclusion, and if possible, upperbody functioning is another domain that should be considered for inclusion. There have been efforts to generate internationally comparable and tested questions, notably by the Washington Group.

# **_Washington Group Short Set_**

Specifically, the Washington Group has developed and tested a set of six questions, also known as the Washington Group Short Set (WGSS). The WGSS’ strength is in its brevity and is wellsuited for use in censuses and national surveys. In conjunction with other data collected on outcome indicators (access to education or employment), it additionally helps to inform policy on equalization of opportunities. It starts with an optional introduction as follows: “The next questions ask about difficulties you may have doing certain activities because of a health problem.” It then has questions covering six different domains as follows: 1. Do you have 5