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 inform the development and implementation of future policies and practices that will reduce childhood poverty.

The sampling approach adopted for the Young Lives study is known as a sentinel site surveillance system. In Vietnam the Young Lives team used multi-stage, purposive and random sampling to select the two cohorts of children. This methodology randomised households within a study site while the sites themselves were chosen based on predetermined criteria, informed by the objectives of the study. To ensure the sustainability of the study, and for resurveying purposes, a number of well-defined sites were chosen. The selection of sentinel sites in Vietnam followed a complex consultative process in which five ?representative? regions were selected on the basis on the regional and urban/rural differences present in modern Vietnam. Next, four communes from each region were selected using a pro-poor selection rule based on the poverty ranking of each commune.

This paper assesses the sampling methodology by comparing the Young Lives sample with larger, nationally representative samples. In doing this, the Vietnam team sought to:

analyse how the Young Lives children and households compare with other children in Vietnam 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 Vietnam determine whether different levels of living standards are represented within the dataset.