data sets have questions on functional difficulties that differ from the WGSS are shown in Table 2.1. Six data sets are censuses that do not cover all six domains: Dominican Republic, Panama, Rwanda, Tanzania, Vanuatu, and Vietnam.

The questions could have wording that differed from the WGSS formulation. If they do, they are shown in Table 2.1. For instance, in South Africa’s 2010 Census, the walking question is worded differently: "Walking _a kilometer_ or climbing a flight of steps" and the cognitive domain is covered by two separate questions for remembering and concentrating. Another example is that of the 2010 Census in Indonesia, which grouped the cognitive and communication domains in one question: "Do you have difficulty remembering, concentrating, or communicating with others due to a physical or mental condition?" Five censuses have a yes/no answer scale: Dominican Republic, Mexico, Panama, Philippines, Rwanda.<sup>1</sup> Meanwhile, Indonesia has only three-level scale: ‘no difficulty’, ‘slight’, and ‘severe’. Tanzania, and Vietnam’s answer scales refer to ‘a little difficulty’ instead of ‘some difficulty’. For the Papua New Guinea HIES, the answer scale is reversed from that in the WGSS as follows: 1. Cannot at all, 2. A lot of difficulty 3. Some difficulty 4. No difficulty.

Only in few data sets (e.g. Ethiopia LSMS) does each individual in the household consistently answer about his/her functional difficulties. In the other countries, it is the household respondent who answers on behalf of every individual in the household.

Three HIES, two LFS, five LSMS, and two general surveys (Afghanistan and South Africa) under study have adopted the WGSS questions to the letter. Event for this subgroup of countries, caution is needed while comparing results across countries. What people may understand from the questionnaire and how they reply could differ given different languages,<sup>2</sup> , cultures, interviewer training and other contextual factors in ways that are beyond the purview of the researchers. Although the functional difficulty questions are worded the same way, there are a few differences in the questionnaires of these five countries. Ethiopia, Malawi, Nigeria, and Tanzania have the WGSS as part of a longer health section in the questionnaire, while Uganda has a separate section titled ‘disability’ after the health section. Tanzania has a somewhat different answer scale including an additional category, no difficulty with assistive devices as follows: 1 - no difficulty, 2 – no difficulty with assistive devices, 3 - some difficulty, 4 – a lot of difficulty and 5 - unable to do. Categories 2 and 3 were collapsed into one category (no difficulty) for comparability with other countries. Although these differences between surveys may seem minor, such minor changes in question wording or in the placement of the question may significantly affect the resulting estimates (Mathiowetz 2001).

Finally, while the WGSS was initially developed for use in censuses among those 5 years of age and older, the six domains may not be adequate to capture disability among children (Loeb et al 2018). We therefore calculate disability indicators only for adults who are 15 years old and older, and their households.

> 1 The answer scale is in fact:  No difficulty, Partial difficulty, Large difficulty, Complete difficulty. However, the IPUMS data set under use in this study only has a yes/no answer.

> 2 The WG has a translation protocol to help preserve the meaning of the questions, but it is not known whether that protocol was used for the data sets with the WGSS.

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