From 1972 to 1977 Zapf was a member of the Steering Committee of the Center for Social Indicators of the Social Science Research Council (SSRC) in Washington, D.C. Zapf is furthermore a member of the ISQLS.
Von 1972 bis 1977 war Zapf Mitglied des “Steering Committee des Center for Social Indicators” des Social Science Research Council (SSRC) in Washington, D.C. Zapf ist außerdem Mitglied der ISQOLS.