## 2.2 Cohort descriptions

The cohorts have different designs, age ranges and assessment instruments. Figure 2.2 displays the age range of developmental assessments per cohort, coloured according to the instruments.

A brief description of each cohort follows:

The Bangladesh study (GCDG-BGD-7MO) was an impact evaluation study including 1862 children around the age of 18 months. The Bayley Scale for Infant and Toddler Development-II (by2) was administered and long-term follow-up data were available for the Wechsler Preschool and Primary Scale of Intelligence (WPPSI) at 5 years .

The Brazil 1 study (GCDG-BRA-1) was a birth-cohort with 3 measurement moments: 644 children at 3 months, 1412 children at 6 months and 1362 children at 12 months. The investigators administered the Denver Developmental Screening Test-II (den) in each round. Long-term follow-up data were available for the Wechsler Adult Intelligence Scale (WAIS) at 18 years .

The Brazil 2 study (GCDG-BRA-2) was a birth-cohort with measurements of 3907 children at 12 months and 3869 children at 24 months. Both occasions collected data on the Battelle Development Inventory (bat) .

The Chile 1 study (GCDG-CHL-1) was an impact evaluation study of 128 children assessed at 6 months, 1732 children at 12 months and 279 at 18 months. The by1 was administered at each of the three waves. Long-term follow-up data were available for the WPPSI at 5-6 years .

The Chile 2 study (GCDG-CHL-2) consists of a birth-cohort of 4869 children. The investigators measured child development by the Battelle Developmental Inventory (bat) at 7-23 months. A total of 9201 children aged 24-58 responded to the Test de Desarrollo Psicomotor (tep) at 24-58 months. For the latter group, follow-up data were available for the Peabody Picture Vocabulary Test (PPVT) at 5-6 years .

The China study (GCDG-CHN) was an impact evaluation study that contained 990 children assessed with the by3 at 18 months .

The Colombia 1 study (GCDG-COL-LT45M) was an impact evaluation study that comprised two waves. Wave 1 contained 704 children at 12-24 months and wave 2 631 children at 24-41 months. The by3 was administered at each wave. Long-term follow-up data were available for PPVT at 4-6 years .

The Colombia 2 study (GCDG-COL-LT42M) was an instrument validation study where all 1311 children aged 6-42 months were measured the by3. Also, there are data for a subgroup of 658 children on den, the Ages and Stages Questionnaire (aqi), and the bat screener. Long-term follow-up data were available for the Fifth Wechsler Intelligence Scale for Children (WISC-V) and the PPVT .

An impact evaluation study in Ecuador (GCDG-ECU) yielded data from 667 children between 0-35 months on the Barrera Moncada (bar). Long-term follow-up data were available for the PPVT at 5-8 and 9-12 years .

The Ethiopia study (GCDG-ETH) was a birth-cohort with 193 children of 12 months in the first wave, 440 children of 30 months at the second wave, and 456 children of 42 months at the third wave. The investigators used the same instrument (by3) for all waves. Long-term follow-up data were available for the PPVT at 10-11 years .

The Jamaica 1 study (GCDG-JAM-LBW) was an impact evaluation study that collected data on the Griffiths Mental Development Scales (gri) for 225 children aged 15 months (first wave), and 218 children of aged 24 months (second wave). Long-term follow-up data were available for WPPSI and PPVT at 6 years .

The Jamaica 2 study (GCDG-JAM-STUNTED) was an impact evaluation study with data on the gri for 159 children at 9-24 months, 21-36 months, and at 33-48 months. Long-term follow-up data were available for sbi, Raven’s Coloured Progressive Matrices (Ravens), and PPVT at 7-8 years and the WAIS at 17-18 years .

The Madagascar study (GCDG-MDG) was an impact evaluation study that used the sbi for 205 children aged 34-42 months. Long-term follow-up data were available for sbi and PPVT at 7-11 years .

The Netherlands 1 study (GCDG-NLD-SMOCC) was an instrument validation study with a total of 9 waves. At each wave the Dutch Developmental instrument (ddi) (In the Netherlands known as Van Wiechenschema) was administered. The first wave included 1985 children at 1 month, wave 2 1807 children at 2 months, wave 3 1963 children at 3 months, wave 4 1919 children at 6 months, wave 5 1881 children at 9 months, wave 6 1802 children at 12 months, wave 7 1776 children at 15 months, wave 8 1787 children at 18 months, and wave 9 1815 children at 24 months .

The Netherlands 2 study (GCDG-NLD-2) was an instrument validation study with a total of five waves. This study resembles GCDG-NLD-SMOCC but for older children. Wave 1 included 1016 children at 24 months, wave 2 995 children at 30 months, wave 3 1592 children at 36 months, wave 4 1592 children at 42 months, and wave 5 1024 children at 48 months .

The South Africa study (GCDG-ZAF) was a birth cohort with four waves. The first wave included 485 children and second wave 275 children, who were assessed at 6 and 12 months, respectively, with the by1 and the gri. The third wave included 1802 children and the fourth wave 1614 children, assessed at 24 and 48 months, respectively, with the Vineland Social Maturity Scale (vin) .