ragin has made many contributions to sociology. he is a proponent of using fuzzy sets to bridge the divide between quantitative and qualitative methods. his main interests are methodology, political sociology, and comparative-historical research, with a special focus on such topics as the welfare state, ethnic political mobilization, and international political economy. he is also the author of more than 100 articles in research journals and edited books, and he has developed software packages for set theory analyses of social data, qualitative comparative analysis (qca) and fuzzy set qualitative comparative analysis (fsqca).