From questionnaire to database: field work experience in the "Immigration, work and health survey" (ITSAL Project)

objective: despite the need for information in the area of migration and health, the available data are sparse. we describe the field work in a cross-sectional study on the health of immigrant workers in spain. method: a convenience sample of workers from colombia, ecuador, morocco and rumania in four cities was targeted, using a block-walking approach. the outcome rates of the american association of public opinion research were estimated. results: of 6,504 persons approached, 71.4% were eligible contacts. of these contacts, only 57.8% completed interviews. response and cooperation rates were above 50%. conclusions: block-walking enabled surveyors to access difficult-to-reach groups. the use of specifically trained surveyors with a background similar to that of the target population increased the effectiveness of our methods.