Two-dimensional properties of autism in different settings. The first one (the case spectrum) in clinical settings is designated as a small skewed distribution (black) at the bottom right of the figure. The other (the whole dimension) in population settings is located at the top of the figure, which has a sigmoid relationship with social vulnerability and involves both nonautistics and autistics as described in text. Under this liability-probability model, the vulnerability is low but not zero in the majority (white part), modest in the border zone (grey), and very high but not the maximum in the extreme tail (black).