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Idealized shapes of developmental change, with age shown on the X-axis and an index of behavioral expression or level of performance on the Y-axis. (a) Linear, (b) Accelerating, (c) Asymptotic, (d) Step-like, (e) S-shaped, (f), Variable, (g) Unsystematic, (h) Stair-climbing, (i) U-shaped, (j) Inverted-U-shaped.
