Advances in Longitudinal Survey Methodology

1Refreshment Sampling for Longitudinal Surveys

Nicole Watson¹ and Peter Lynn²

¹Melbourne Institute of Applied Economic and Social Research, University of Melbourne, Melbourne, Australia

²Institute for Social and Economic Research, University of Essex, Colchester, UK

1.1 Introduction

As a longitudinal survey matures, there may be a need to consider refreshing the sample by adding a new sample (or indeed several new samples) to the ongoing sample. This may be due to the impacts of non‐response or attrition on the size or representativeness of the sample, or a desire to increase the size of the overall sample, target (overrepresent) particular segments of population, or provide coverage of new population entrants.

The type of longitudinal population that the longitudinal survey aims to represent is integral to this discussion of refreshing the sample. Figure 1.1 shows the various elements of the population as it changes from when the sample was originally selected in wave 1 to a later time point, wave t. People leave the population via death or otherwise moving out of scope (i.e. by emigrating or ageing out of the population of interest) and others join the population as new births (or by ageing into the population of interest) or otherwise moving in‐scope (such as immigrating). The terms ‘births’ and ‘deaths’ are used in this chapter to refer to this broader group of population joiners and leavers, respectively. Smith et al. (2009) describe three types of longitudinal populations: ...