YOU need a brief measure, say, of stress, or social resources, or functional status. You find one that not only seems to address the conceptual issues about which you are concerned, but for which information on validity and reliability have also been published. Moreover, it has been used frequently, and its name is well recognized. You are happy—you know you have done the right thing. But have you? Perhaps, and up to a certain extent; but not necessarily. The article by Burholt and colleagues (this issue) is an important reminder that an assessment developed in one location, or with a particular sample, may perform differently in another location and with a different sample. They wished to measure social resources, a complex concept, using a minimum number of items. They selected the Social Resources measure developed in the United States for the Older Americans Resources and Services questionnaire because of its theoretical basis, statistically and clinically sound selection of items, and established reliability (‘‘gold standard’’ validity had not been assessed because the ‘‘gold standard’’ had already been incorporated). They then did what few people do—they gathered data to check whether this measure was understood equally well in the six developed countries of Europe in which they were interested. They identified some serious problems. Using comparable sampling frames in each country and similar modes of administration (face-to-face-interviews, except for one site where mailing was preferred), they found major differences in participation rate. There appeared to be no obvious explanation for why the participation rate was so low in some countries but much higher in others. All questions but one were well accepted, but the question concerned with the availability and likely duration of help when sick was problematic and had a high nonresponse rate. In a country such as Sweden, where substantial formal resources are available (reflecting the preference of the population), this item appeared to lose the meaning it had in the United States, where support may be needed from (and expected of) family and friends in preference to formal resources. Although the factor structure of the Older Americans Resources and Services social resources section still held overall, it held with distinctly less strength than in the original.