Thirty-five years ago, the four authors of this book addressed the problem of validity in social science research. This revised edition builds on the earlier version's drive to justify novel techniques of survey and archival research. Richly illustrated throughout, the purpose of this book is to authorize and motivate ingenuity in obtaining information. The authors combine very different methods so that research results can withstand the `threats to validity' which so frequently invalidate single-measure, conventional research.