An Assessment of the Young Lives Sampling Approach in Peru
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Young Lives is a longitudinal research project investigating the changing nature of childhood poverty. The study is tracking the development of 12,000 children in Ethiopia, Peru, India (Andhra Pradesh) and Vietnam through qualitative and quantitative research over a 15-year period. Since 2002, the study has been following two cohorts in each study country. The younger cohort consists of 2,000 children per study country aged between 6 and 18 months in 2002. The older cohort consists of 1,000 children per country aged between 7.5 and 8.5 in 2002. The key objectives of Young Lives are: (i) to improve the understanding of causes and consequences of childhood poverty, (ii) to examine how policies affect children's well-being and (iii) to inform the development and implementation of future policies and practices that will reduce childhood poverty. In Peru the Young Lives team used multi-stage, cluster-stratified, random sampling to select the two cohorts of children. This methodology, unlike the one applied in the other Young Lives countries, randomised households within a site as well as sentinel site locations. To ensure the sustainability of the study, and for resurveying purposes, a number of well-defined sites were chosen. These were selected with a pro-poor bias, ensuring that randomly selected clusters of equal population excluded districts located in the top five per cent of the poverty map developed in 2000 by the Fondo Nacional de Cooperacion para el Desarrollo (FONCODES, the National Fund for Development and Social Compensation). This paper assesses the sampling methodology by comparing the Young Lives sample with larger, nationally representative samples. The Peru team sought to: analyse how the Young Lives children and households compare with other children in Peru in terms of their living standards and other characteristics, examine whether this may affect inferences between the data, establish to what extent the Young Lives sample is a relatively poorer or richer sub-population in Peru, determine whether different levels of living standards are represented within the dataset. The report used two nationally representative comparison samples: the Living Standard Measurement Survey 2001 (ENAHO 2001) and the Demographic and Health Survey 2000 (DHS 2000). The document used two different methodologies to assess the Young Lives sample. The document first compared poverty rates calculated for Young Lives and the ENAHO 2001, then compared wealth index scores for the Young Lives households with those for DHS 2000 households. This provided a graphical illustration of the relative wealth of the Young Lives sample relative to the population of Peru. The researcher went on to use standard t-tests to test for statistical significance of the differences in several living standard indicators between Young Lives, the DHS 2000, and the ENAHO 2001 samples. Finally, the authors investigated potential biases in the Young Lives and DHS 2000 samples by comparing these with the Census 2005. The study compared variables that are common in the Census 2005, the DHS 2000, and Young Lives – area of residence, access to electricity and access to drinking water. In order to ensure comparability of the different samples the report imposed constraints on the comparison samples to accommodate the fact that the Young Lives sample only includes households with at least one child aged between 6 and 18 months. The researchers found that the poverty rates of the Young Lives sample are similar to the urban and rural averages derived from the ENAHO 2001. Households in the Young Lives sample were found to be slightly wealthier than households in the DHS 2000 sample. A similar picture emerged when the authors use unweighted t-tests to compare the means for a range of living standard indicators between the Young Lives and the DHS 2000 samples. Young Lives households own more private assets and have better access to public services such as drinking water and electricity supply. Similarly, members of households in the Young Lives sample are better educated and have better access to vaccinations and prenatal care than DHS 2000 households. To establish the existence of biases in the Young Lives and the DHS 2000 samples the authors compared both with data from the Census 2005. It was evident that the Young Lives sample includes households with better access to electricity and drinking water than the Census 2005.