Sampling for qualitative research using quantitative methods .1. Measuring GPs' attitudes towards discussing smoking with patients

Background. Interview studies which employ qualitative methodology are often concerned with classifying behaviours or attitudes and an ideal sample of research subjects displays variety in the attitudes or behaviours under scrutiny. Objective. This paper describes the development of a questionnaire which measures GPs' attitudes towards discussing smoking with patients with the intention of using this instrument to select GPs with diverse views for a qualitative interview study. Method. Thirteen attitude statements with an accompanying Likert-type scale were completed by 327 GPs in one FHSA area. Factor analysis of responses produced two subscales: 'perceived efficacy' and 'enthusiasm'. Reliability and validity of these were examined. Results. Each subscale had good internal reliability and preliminary exploration of construct validity supported the notion that the subscales were valid. Conclusion. The use of this type of instrument in sampling GPs for qualitative studies could be effective for selecting subjects with a diversity of views towards the research topic.