@book{ Solr-27373427X, title = {Validity in survey research: with special reference to the techniques of intensive interviewing and progressive modification for testing and constructing difficult or sensitive measures for use in survey research; a report}, author = {Belson, William A.}, editor = {Cleland, J. G. and Cleland, J. G.}, address = {Aldershot u.a.}, publisher = {Gower}, year = {1986}, }