The good news:
Derived from “Union Membership, Coverage, Density, and Employment Among Private Sector Workers, 1973-2010,” © 2010 by Barry T. Hirsch and David A. Macpherson.
Why is this good news? Read on: “The Truth about Labor Day,” from the Ludwig von Mises Institute; “Toward a Capital Theory of Value,” “A Very Politically Incorrect Labor Day Post,” and “Your Labor Day Reading,” by me. (NB: Some of the links in these old posts may be broken, and some of the quoted Wikipedia articles may have been revised by “contributors” eager to whitewash the labor-union movement.)