Tracking in Panel Survey shows that failure to follow movers in longitudinal surveys results in higher rates of Household Surveys attrition, including attrition selected on both observed and unobserved characteristics, which By Firman Witoelar complicates inferences. Clearly, inferences based Sample attrition is an inherent challenge faced by on these kinds of panel data need a theory (and longitudinal household surveys. Attrition in preferably, evidence) of where the missing household surveys can occur as a result of respondents went, and why. migration, respondents’ refusal to participate, as well as death. In countries where mobility is high, Failure to follow movers entails scientific costs in research findings suggest that longitudinal terms of higher attrition rates stemming from household surveys should seriously consider both observed and unobserved characteristics. tracking respondents who move, particularly The scientific costs of not following the movers those who move outside the baseline locality. must be weighed against the financial costs of tracking. These financial costs will vary according Why Track the Movers? to survey design and setting, but can be minimized with careful planning and the use of Survey planners conducting follow-up interviews innovative technology. as part of a longitudinal household survey need to decide whether to follow households and individuals who have left their baseline location, Defining Targets and Boundaries and to what degree with respect to time, As respondents leave their baseline household, distance, and cost. People who move are unlikely the remaining sample of non-movers becomes to be a random subset of the baseline less representative of the baseline, particularly as respondents, and they are likely to have certain migration is unlikely to be random. Survey characteristics that differ from those who remain planners must define the respondents that are to at the baseline location. Following these movers be tracked (tracking targets), as well as those that and interviewing them minimizes the attrition are to be interviewed (interviewer targets). rate and addresses potential selectivity biases in Depending on the aim of the study, the survey non-random attrition. might track all individuals such that the next round of the survey is representative of the Earlier work on panel attrition provides some baseline of individuals. Alternatively, the survey methods to assess the extent of attrition bias by could follow only individuals with certain examining selection on observed characteristics. characteristics. Survey planners may not wish to When the observed baseline characteristics of track everyone, and they may also choose to those who move are different from those who interview people not in the baseline (such as remain, there are clearly strong incentives to returned migrants and other new household track movers. However, new studies suggest that members). even if the observed baseline traits are not different, researchers should still be concerned Once the survey planners have determined the about analyzing a panel of households restricted tracking targets, a set of tracking rules simple to non-movers. A recent study by Thomas et al. enough for interviewers to follow during (2011) on attrition in the Indonesia Family Life fieldwork should be established. One of the rules should involve setting the boundaries on the Living Standards Measurement Study Brief Series www.worldbank.org/lsms-isa distance to which individuals will be tracked. teams may be assigned to find respondents (or a Possible boundaries include administrative sub-sample of them) who have moved, after the borders or a simple distance limit. end of the main survey effort. Some surveys do a combination of both. Organizing Tracking Operations Difficulties with tracking often result from Flexibility for Innovation problems concerning the collection or utilization In addition to careful consideration and planning, of information on respondents’ new locations. a successful tracking operation also requires After tracking targets have been defined, field flexibility to new innovative approaches. When experience suggests that the implementation of available, official records such as birth, marriage successful tracking requires a tracking manager or death records, either in the baseline location or management team whose sole responsibility is or in the destination, can be useful in finding to manage the tracking aspects of the survey. individuals’ whereabouts. Some surveys have This includes managing the tracking information used photographs of respondents to increase re- system, evaluating the quality of tracking contact rate in future survey rounds. When information from the field, as well as resolving applicable, GIS data can be used to track back conflicting information about respondent households that are hard to locate. The use of location. In a resource-constrained environment, computer-assisted personal interviewing (CAPI), the tracking manager must also organize and which offers potential advantages over pencil- prioritize the tracking cases by evaluating the and-paper interviewing, can also be extended to trade-offs between cases before the tracking tracking. CAPI facilitates the use of photographs cases are assigned to the teams in the field. and geo-codes, and can reduce the time needed to collect tracking information and send it to the Tracking Forms and Protocol survey headquarters. As timing and coordination To implement tracking in the field, interviewers of different teams is critical in organizing tracking must follow the established tracking protocol. activities, CAPI has the potential to make a The protocol should identify the individuals to be significant impact on the success of tracking. tracked, describe how to collect information about the tracking targets using a well-designed Ethical Concerns tracking form, and establish the method for Finally, it is essential to ensure that the ethical relaying the information back to the survey implications of tracking activities are carefully headquarters. The type and the quality of considered. Since numerous types of information information collected will be crucial in finding necessary to find the respondents are collected, respondents at their new location. Information care must be taken to protect the privacy of the collected may include new address, new work respondents. Some form of informed consent address, phone numbers, locations that the should also be obtained. One option is to obtain mover used to frequent, and the names and consent only for the baseline survey, while addresses of people that the mover knows at the explaining the nature of longitudinal surveys and destination. The interviewers must also be informing the respondents that they will be equipped with information about respondents visited and asked for consent again in the future. gathered from the baseline survey or the previous round, such as old workplaces, old This brief is based on: Witoelar, Firman (2010). employers, and schools that the mover attended. Tracking in longitudinal household surveys. What this implies is that even at the baseline LSMS-ISA Working Paper, Washington D.C.: The survey, survey planners must plan for the World Bank. The full paper is available for collection of information that may be useful to download at www.worldbank.org/lsms-isa. locate respondents if they move between survey rounds. For more information, please visit: The survey protocol also governs the process www.worldbank.org/lsms-isa that interviewers follow once the tracking information has been collected. In some surveys, Or contact: interviewers may be required to either track the Firman Witoelar, World Bank respondents within the proximity of their survey fwitoelar@worldbank.org area, or transfer the tracking cases to other interviewers who are closer to the destination of the movers. In other surveys, special tracking Living Standards Measurement Study Brief Series www.worldbank.org/lsms-isa