6 The standalone category includes country-specific household surveys such as a Household Budget Survey (HBS) or a Household Income and Expenditure Survey (HIES) (their scope is typically rather similar). Some countries also have a dedicated survey capturing health expenditures and other health-related concerns: the US, for example, has a Medical Expenditure Panel Survey. Access to the microdata from these standalone surveys tends to vary. Some countries provide authorized users with access to the microdata, though in many cases the publicrelease microdata are modified to ensure respondent anonymity. Countries also vary in their policies on who may access the microdata and how: OECD countries like Ireland, the UK and the US have very liberal policies, as do several middleincome countries, like Peru and South Africa, allowing any bona-fide researcher to download the public-release microdata. By contrast, many OECD countries have much tighter access policies, e.g. authorizing only nationals of the country access to the data, and sometimes requiring the user access the data on-site.

The other category in Figure 1 covers multi-country survey collections. These are of two types. The first are genuine multi-country surveys – surveys where there is a fairly standardized questionnaire used in several countries. The World Bank’s Living Standards Measurement Study (LSMS) is an example. The WHO’s World Health Survey (WHS) is another. The former is a multipurpose survey with rich information on household consumption and expenditure across a range of areas, including health, while the latter is a health survey with extensive information on out-of-pocket health expenditures but only very limited information on other expenditures. Access rules to these multi-country data sets vary, sometimes (e.g. the LSMS) varying even across surveys within a collection depending on permissions granted by the relevant government.

The second type of multi-country survey collection consists of country-specific surveys where the questionnaires differ across countries but the data have been harmonized ex post by an agency, such as Eurostat, the Luxembourg Income Study (LIS) (Luxembourg Income Study (LIS) 2019), or the World Bank. Eurostat, for example, every five years takes the raw data from the HBS surveys of the EU member states and produces a harmonized data set for each country with the same constructed harmonized expenditure variables, including out-of-pocket health expenditures. The LIS also produces harmonized data sets based on HBS and HIES surveys for a wide range of countries; some of these have harmonized data on out-ofpocket health expenditures. In both cases, authorized users are able to use only the data set comprising the harmonized variables, not the original data. Several groups within the World Bank also construct harmonized data sets. In the regional World Bank units, the focus is on overall household consumption, the aim being to assist the Bank’s poverty-monitoring work; in this work, the methods used to construct consumption aggregates in the LSMS (Deaton and Zaidi 2002) typically guide the process. Other groups in the World Bank have goals other than facilitating povertymonitoring. One harmonization exercise (the Standardized Household Expenditure Survey (SHES)) is directed at assisting the process of constructing purchasing