4.1 The Dutch Development Instrument (DDI)

4.1.1 Setting

The Dutch Youth Health Care (YHC) routinely monitors the development of almost all children living in The Netherlands. During the first four years, there are 13 scheduled visits. During these visits, the YHC professionals evaluate the growth and development of the child.

The Dutch Development Instrument (DDI; in Dutch: Van Wiechenschema) is the standard instrument used to measure development during the ages 0-4 years. The DDI consists of 75 milestones. The instrument assesses three developmental domains:

1. Fine motor, adaptation, personality and social behaviour;
2. Communication;
3. Gross motor.

The milestones form two sets, one for children aged 0-15 months, and another for children aged 15-54 months. The YHC professionals administer an age-appropriate subset of milestones at each of the scheduled visits, thus building a longitudinal developmental profile for each child.

4.1.2 Description of SMOCC study

The Social Medical Survey of Children Attending Child Health Clinics (SMOCC) study is a nationally representative cohort of 2,151 children born in The Netherlands during the years 1988–1989 (Herngreen et al. 1994). The study monitored child development using observations made on the DDI during nine visits covering the first 24 months of life. The SMOCC study collected information during the first two years on 57 (out of 75) milestones.

The standard set in the DDI consists of relatively easy milestones that 90 per cent of the children can pass at the scheduled age. This set is designed to have maximal sensitivity for picking up delays in development. A distinctive feature of the SMOCC study was the inclusion of more difficult milestones beyond the standard set. The additional set originates from the next time point. The success rate on these milestones is about 50 per cent.

4.1.3 Codebook of DDI 0-30 months

Table 4.1 shows the 57 milestones from the DDI for ages 0 - 30 months as administered in the SMOCC study. Items are sorted according to debut, the age at which the item appears in the DDI. The response to each milestone is either a PASS (1) or a FAIL (0). Children who did not pass a milestone at the debut age were re-measured on that milestone during the next visit. The process continued until the child passed the milestone.