Internationally, there is a drive for equality in health care for ethnic groups. To achieve equality, produce sound policies, and provide appropriately targeted services good quality data are essential. Where data are based upon self report, especially from non-English speakers, there are major barriers to the accumulation of reliable and valid information. When data collection instruments designed for English speakers are simply translated into ethnic minority languages, measurement error can result from inadequate translation procedures, inappropriate content, insensitivity of items, and the failure of researchers to make themselves familiar with cultural norms and beliefs. More attention should be paid to conceptual and cultural factors especially in epidemiological and clinical studies where self report is used to gather data. More interdisciplinary collaboration is necessary as well as a modification of customary methods of data collection and the assumptions behind them. The essence of such modifications entails participatory research with members of the linguistic communities concerned.