5.7 Other modelling actions
5.7.1 Instrument fit
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.
| 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 |