The validity of data from next-of-kin in studies of mortality among migrants

The design of the British-Norwegian Migrant Study afforded a unique opportunity for comparing in a large sample certain items of information on the same individual, as reported by himself some time before death, with the responses on the same points given after his death in a questionnaire addressed to his next-of-kin. This paper describes a comparison of the degree of agreement between these two methods of obtaining data and draws attention to possible sources and directions of bias involved in the use of information supplied after death by the next-of-kin. Validity, as measured by agreement with the subject's own replies, depends in part on the topic and nature of the information required and on the population included in the survey. A built-in check, such as that incorporated in the British-Norwegian Study, confers the advantage that such biases can be identified and the numerical effect of adjusting for them assessed with some confidence.