“…For example, several early researchers equated participants on measures of general cognition or intelligence before examining age differences in the measures of primary interest (e.g., Bromley, 1956Bromley, , 1958Bromley, , 1967Foster & Taylor, 1920;Ruch, 1934;Thorndike et al, 1928). Other early studies included multiple cognitive measures to compare the relative magnitude of age differences across measures (e.g., Bilash & Zubeck, 1960;Birren & Morrison, 1961;Foster & Taylor, 1920;Gilbert & Levee, 1971;Horn, 1967;Jones & Conrad, 1933;Schaie, 1958;Sward, 1945).…”