## 8.1 SMOCC design: Standard and additional milestones

At each visit, the SMOCC study collected scores on a set of standard milestones (that about 90 per cent of the children will pass) and a set of additional milestones (that about 50 per cent of the children will pass). See Section 4.1.2.

The SMOCC dataset covers nine different waves. The set of milestones used in the DDI varies per visit. The number of standard milestones varies between 2 and 7 on various occasions. The additional milestones equal the standard ones from the next wave.

 Age Standard Additional 1m 5 2 2m 2 5 3m 5 6 6m 6 7 9m 7 6 12m 6 6 15m 6 6 18m 6 7 24m 7 7

Table 8.1 summarizes the scheduled age for each wave, the number of standard milestones and the number of additional milestones.

Figure 8.1 shows the subsets of DDI items administered at each age. For example, at the 1-month visit, the five standard milestones are ddicmm029 - ddigm056, and the two additional ones are ddicmm030 and ddifmd002. At the 2-month visit, the standard milestones are ddicmm030 and ddifmd002, and the five additional ones are ddicmm031 - ddigmd057. And so on.