As previously quoted, Bollen criticized previous studies of Freedom in the World as anecdotal and inconclusive; they raised issues needing further study by scientific methods rather than anecdotes.[4] Bollen studied the question of ideological bias using multivariate statistics. Using their factor-analytic model for human-rights measurements, Bollen and Paxton estimate that Gastil's method produces a bias of -0.38 standard deviations (s.d.) against Marxist–Leninist countries and a larger bias, +0.5 s.d., favoring Christian countries; similar results held for the methodology of Sussman (Bollen and Paxton, 2000, p. 585).[22] In contrast, another method by a critic of Freedom in the World produced a bias for Leftist countries during the 1980s of at least +0.8 s.d., a bias that is "consistent with the general finding that political scientists are more favorable to leftist politics than is the general population" (Bollen and Paxton, p. 585).[22]