Trajectories of number of sexual partners from ages 16–18 and 20–22 (N = 527). At ages 16–18 and 21–22, number of sexual partners was measured as 0 = none, 1 = 1 partner, 2 = 2 to 3 partners, and 3 = more than 3 partners in last 12 months; at age 20, number of sexual partners was measured as 0 = none, 1 = 1 to 2 partners, 2 = 3 to 6 partners, and 3 = more than 6 partners in last 24 months. Fit indices of three-class model: BIC = 5958.96, Entropy = .91.