## 2.1 Overview of cohorts and instruments

The Global Child Development Group (GCDG) collected longitudinal data from 16 cohorts. The objective of the study was to develop a population-based measure to monitor early child development across ages and countries. The requirements for inclusion were

1. direct assessment of child development;
2. availability of individual milestone scores;
3. spanning ages between 0-5 years;
4. availability of follow-up measures, at ages 5-10 years.

The effort resulted in a database containing individual data from over 16,000 children from 11 countries. The world map below (Figure 2.1) colors the countries included in the study. Section 2.2 briefly describes each cohort. Section 2.3 reviews the measurement instruments.

The GCDG data comprises of birth cohorts, impact evaluation studies and instrument evaluation studies. Table 2.1 displays a brief overview of the instruments used in each sub-study.

Table 2.1: Overview of instruments administered in the cohorts.
Cohort by den gri bat vin ddi bar tep aqi sbi
Brazil 1 x
Brazil 2 x
Chile 1 x
Chile 2 x x
China x
Colombia 1 x
Colombia 2 x x x x