Triaxial model for discussing prognosis in ASD. Age is represented on the x-axis, with birth at the origin. Thex-axis to the left of the origin is indicated as a dotted line, because no child's age is less than zero. Intelligence is represented on the y-axis, with an IQ of 70 (the cutoff for MR) at the origin; children above the imaginary horizontal plane running through the origin have IQs in the normal range, whereas children below this plane have MR. Degree of atypical behavior, ranging from severe to mild, is depicted on the z-axis, with diminishing severity running into the plane of the paper.
Child A represents an individual with severely atypical behavior plus MR. The cube represents the magnitude of the individual's clinical deficit, which is a compound of ASD plus MR. As this person ages, he or she continues to manifest a readily recognizable symptom complex consistent with the diagnosis of ASD plus MR. Child B represents an individual whose atypical features are moderate to mild, and whose general intelligence is average or better. As such an individual ages, the core features of ASD break up into isolated fragments, which diminish in severity with the passage of time. Other combinations (severely atypical behavior with normal intelligence; severe MR with mildly atypical behavior) are also possible, but not shown.