## 4.2 Probability of passing a milestone given age

Figure 4.1: Empirical percentage of passing each milestone in the DDI against age (Source: SMOCC data, $$n$$ = 2151, 9 occasions).

Figure 4.1 summarizes the response obtained on each milestone as a curve against age. The percentage of pass scores increases with age for all milestones. Note that curves on the left have steeper slopes than those on the right, thus indicating that development is faster for younger children.

The domain determines the coloured (blue: gross motor, green: fine motor, red: communication). In general, domains are well mixed across age, though around some ages, e.g., at four months, multiple milestones from the same domain appear.