Experimental Design
In 1986-1987, the Jamaican Study enrolled 129 stunted children age 9-24 months that lived in poor disadvantaged neighborhoods of Kingston, Jamaica. Stunting was defined as having a standardized height for age z-score less than -2. The children were stratified by age (above and below 16 months) and sex. Within each stratum, children were sequentially assigned to one of four groups using a randomly generated seed to begin the assignment. The four groups were (1) psychosocial stimulation (N=32), (2) nutritional supplementation (N=32), (3) both psychosocial stimulation and nutritional supplementation (N=32), and (4) a control group that received neither intervention (N=33). All children were given access to free health care regardless of the group to which they were assigned.
The stimulation intervention (comprising groups 1 and 3) consisted of two years of weekly one-hour play sessions at home with trained community health aides. The curriculum for the cognitive stimulation was based on Piagetian concepts. Mothers were encouraged to converse with their children, to label things and actions in their environments and to play educational games with their children. Particular emphasis was placed on language development, the use of praise, and on improving the self-esteem of both the child and of the mother. At age 24 months, the curriculum was enriched to include concepts such as size, shape, position, quantity, color, etc. based on the curriculum in Palmer.
The focus of the weekly play sessions was on improving the quality of the interaction between mother and child. Mothers were encouraged to continue practicing the activities and games learned during the visits on a continuing basis beyond the home visitation time. At every visit, homemade toys were brought to the home and left for the mother and child to use until the next visit when they were replaced with new ones. The intervention was innovative both for its focus on activities to promote cognitive and language development and for its emphasis on direct mother-child interactions. The nutritional intervention (comprising groups 2 and 3) was aimed at compensating for the nutritional deficiencies that may have caused stunting. The nutritional supplements were provided weekly for a two-year period. The supplements consisted of one kilogram of formula containing 66% of daily-recommended energy (calories), and 100% of daily-recommended protein. In addition, in an attempt to minimize sharing of the formula with other family members, the family also received 0.9 kilograms of cornmeal and skimmed milk powder. Despite this, sharing was common and uptake of the supplement decreased significantly during the intervention.
Of the 129 study participants, two of the participants dropped out before completion of the two-year program. The remaining 127 participants were surveyed at baseline, resurveyed immediately following the end of the two-year intervention, and again at ages 7, 11, and 18. Our analysis is based on a re-interview of the sample in 2007-08 when the participants were approximately 22 years old, some 20 years after the original intervention.
For comparison purposes, the study also enrolled a sample of non-stunted children from the same neighborhoods, where non-stunted was defined as having a height for age z-score greater than -1 standard deviations. At baseline, every fourth stunted child in the study was matched with one non-stunted child who lived nearby and was the same age (plus or minus 3 months) and sex. At age 7, this sample of 32 was supplemented with another 52 children who had been identified in the initial survey as being non-stunted and fulfilled all other inclusion criteria. While the non-stunted group was better off than the stunted group in terms of their personal development and their socioeconomic status, the non-stunted children were still living in the same economically and socially disadvantaged Kingston neighborhoods. Members of the non-stunted comparison group did not receive any of the interventions, but did receive the same free health care as those in the stunted experimental group. From age 7 onwards, this group was surveyed at the same time as the participants in the experiment. This sample is used to investigate the extent to which the early childhood stimulation intervention helped to compensate for initial disadvantage by comparing the stunted treatment group with the non-stunted external comparison group. We define complete catch-up as no difference between the treated stunted group and the non-stunted comparison group.
In order to better understand the external validity of the catch-up analysis we compare the non-stunted group to the general population using data from two surveys that are representative of urban Jamaica: (1) the 1992 Jamaican Survey of Living Conditions (JSLC) that was collected when the children were 7 years old and when most of the non-stunted sample was first surveyed, and (2) the 2008 Jamaica Labor Force (JLF) survey that was collected in the same year as the last follow-up. Unfortunately the labor supply and earnings questions in the JLF and in our survey were asked in different ways, and there was a 50% non-response rate in the JLF to the earnings questions among those who were employed. Only the education variables are directly comparable.