The Boston participants also completed the Boston cognitive battery, in person, in about 90 minutes, within two years (mean = 18 months) after the BTACT was administered. The Boston cognitive battery includes four factors based on a confirmatory factor analysis (Miller & Lachman, 2000 ) using the cognitive tests which were administered at both Time 1 and Time 2. The factors and their test markers are Short-term Memory [measured with Forward Digit Span, Backward Digit Span (from Wechsler Adult Intelligence Scale, WAIS, Wechsler, 1955 ) and Serial 7s (Folstein et al., 1975 (link))], Verbal Ability (WAIS, Vocabulary, Wechsler, 1955 ), Reasoning [Letter Series (Schaie, 1985 ) and Ravens Advanced Progressive Matrices (Raven, Raven, & Court, 1991 )], and Speed [Letter Comparison (Salthouse, Kausler, & Saults, 1990 ) and Digit Symbol Substitution (Wechsler, 1955 )]. Factor scores for each factor were computed as the mean of the z-scores for the measures in that factor. Additional measures given to a subset of the sample at Time 2 included: the "How Many, What Number" task switching (Cepeda et al., 2001 (link)), trail-making (Reitan, Wolfson, Wedding, Horton, & Webster, 1986 ), letter number sequencing (Wechsler, 1997 ), and logical memory (Wechsler, 1997 ).