The Federal Government has long recognized the value in attempting to introduce some level of standardization of disability measures into national survey efforts. For example, in 1988 the Forum on Aging-Related Statistics systematically examined surveys measuring ADLs to identify reasons for variation in estimates (Wiener et al. 1990). Most recently, the Federal Interagency Forum on Aging-Related Statistics has recommended that surveys that have ADL, IADL, and other measures of physical functioning use consistent wording and response categories whenever possible. Standardization of disability questions across countries has also received attention, as illustrated in a recent draft position paper by the Washington Group (Madans et al. 2004). The authors make the important point that measures may need to vary to suit different purposes, but they also argue for the need to standardize disability questions across countries as much as possible.
Related to this notion of standardization is the challenge of identical words not providing a shared meaning for all groups. For example, the term disability or even difficulty may not carry the same meaning across countries or across cultures within a country. The use of anchoring vignettes has received recent attention as a means of improving comparisons across groups or countries of survey-based measures of health (Salomon et al. 2004; King et al. 2004) and disability (Banks et al. 2004; Kapteyn et al. 2004; Tourangeau et al. 2005). The approach involves including in surveys a self-assessment of respondents health (or disability) and an assessment of several hypothetical persons health, as described in short vignettes. The anchoring vignettes for measuring self-care in the World Health Study, for example, are shown in Table 2. Because the vignettes measure the variation in concepts for a set of specific circumstances, they answers may be used to standardize or anchor differences in perceptions across groups or countries (see King et al. 2004 for a description of methodological approaches).