[image: EXCERPT] In studies of the state of the labor unions, researchers often estimate *union membership attrition*—that is, the annual loss in union members caused by employment shifts. For unions to have net growth in the number of members, the losses must be offset by new union members, which are gotten through organizing. This research summary examines the validity of common assumptions about membership attrition by measuring union membership changes in expanding and declining industries as well as the number of new members needed by the unions each year for either no change or an increase in union density of 1 percentage point. Union density, a widely used measure of union organization and influence, is calculated as the annual percentage of employed wage and salary workers who are union members.

http://www.bls.gov/opub/mlr/2010/01/art4exc.htm