5.7 Other modelling actions

5.7.1 Instrument fit

Box plot of the distribution of item outfit per instrument in model 1339_11.

Figure 5.6: Box plot of the distribution of item outfit per instrument in model 1339_11.

Some instruments fit better than others. Figure 5.6 shows the box plots of outfit per instrument. Instruments bar, by1, ddi and vin generally fit well, whereas discrepancies between model and data are larger for bat, by2 and sbi. Through additional modelling, we found that it was extremely difficult to get enough high-quality bridge items that could link bat (Battelle Development Inventory) to the other instruments. We also found that models without the Battelle were able to better discriminate children in the upper range of the D-score scale. We therefore opted to remove bat from the model, even though this meant that one cohort (GCDG-BRA-2) had to be dropped from the analysis.

It is not clear why bat does not fit. Perhaps the scoring system of the Battelle in three categories invokes scoring behaviour that is different from the PASS/FAIL scoring used by most other instruments, even though this appears to be less of a troublesome aspect in aqi, which also uses three response categories.

5.7.2 Splitting, combining and selecting equate groups

Most of the modelling effort went into finding a set of high-quality equate groups that link the instruments. For example, we tried to bridge the South-African study placing vinxxc016 (uses a short sentence) into EXP26 (two-word sentences) and EXP36 (sentences of 3 or more words), but neither option led to a reasonable model. On the surface, milestone by3gmd060 (balances on right foot, 2 seconds) appears to fit within GM60 (balances on foot), but the analysis showed large discrepancies with the other items in the groups, so it had to be taken out.

Subject-matter experts identified 38 items that were thought to be cross-culturally incompatible. Table 5.1 provides an overview. Many of such milestones involve a specific language concept (such as a pronoun), refer to stairs (less common in rural settings), help in house or clothing behaviour. These items have different meanings in different contexts, so they were not used to bridge instruments.

Table 5.1: Milestones not used for equating because of limited cross-cultural validity
Item Label
aqislc023 When you dress your baby does she lift her foot for her shoe, sock, or pant leg?
aqislc041 Using these exact words, ask your child, “Are you a girl or a boy?” Does your child answer correctly?
by1mdd050 Washes and dries hands
by1pdd053 Bowel and bladder control
by1pdd054 manipulates table edge actively
by2pdd069 Walsk up stairs with help
by3cgd043 Walks down stairs with help
by3cgd052 Walks down stairs with help
by3gmd047 Clear Box: Front
by3gmd049 Clear Box: Sides
by3gmd057 Uses pronouns
by3gmd058 Walks Up Stairs Series: Both feet on each step, with support.
by3red030 Walks Down Stairs Series: Both feet on each step, with support
by3exd030 Walks Up Stairs Series: Both feet on each step, alone.
barxxx016 Walks Down Stairs Series: Both feet on each step, alone
barxxx020 Understands pronouns (him, me, my, you, your)
dengmd020 Eats with spoon without help (M; can ask parents)
densld012 Takes off shoes and socks (M; can ask parents)
densld013 Can dress (one piece) (M; can ask parents)
grigmd219 Walk Up Stairs
grigmd222 Drink from a cup
mdsgmd002 help in house
mdsgmd003 (Locomotor) Walks up and down stairs.
mdsgmd004 (Locomotor) Goes alone on the stairs (any method)
mdsgmd005 Hands-and-knees crawling
mdsgmd006 Standing with assistance
ddifmm019 Walking with assistance
ddifmd154 Standing alone
vinxxc002 Walking alone
vinxxc003 chew solid foods
vinxxc009 take off socks / shoes
vinxxc012 get on with other children
vinxxc014 know what’s edible
vinxxc022 walk upstairs
vinxxc028 avoid simple danger - knife / hot
vinxxc031 help around the house / clear table
vinxxc040 Play or do things with other children of same age eg sing song
ddifmm025 Help with little things around the house eg pick up things