# 1. INTRODUCTION

Does the same question that is asked of the same population yield the same answer in face-toface interviews when other parts of the questionnaire are altered? If not, what might be correlated with the discrepancies and what would be the resulting implications for proxy-based poverty measurement? These are the central questions of our study. While the empirical investigation is conducted in the context of predicting household consumption expenditures, our findings are equally relevant for the estimation of trends based on questionnaires that exhibit variations in design over time and for impact evaluations that might rely on questionnaires of different length and complexity for treatment and control samples.

Estimating consumption and poverty via proxies is compelling as consumption measurement is often argued to be complex and costly. The literature on proxy-based poverty measurement highlights the promise of the method in improving the frequency and comparability of interannual poverty estimates at a lower cost, and sometimes by using already existing data (Christiaensen et al., 2012). Related applications on providing intra-year poverty predictions (Douidich et al., 2013), and developing proxy means tests for enhancing the targeting performance of development programs (Houssou & Zeller, 2011) have captured attention. With increasing pressure placed on national statistical systems by governments and the international community for increasing the frequency, quality, and comparability of poverty statistics, the interest in the method’s application for filling the gaps in a cost effective fashion is generating continued interest.

Both parametric and non-parametric approaches to estimation have been featured in the literature.<sup>2</sup> Regardless of the approach, all practical applications would rely on data originating from two non-identical questionnaires: one set of data to establish the underlying model and another set of data with proxies to pair with the model parameters and to obtain predictions. In the case of consumption and poverty, the model is typically established based on data from a multi-purpose household questionnaire that yields a comprehensive welfare aggregate (hereafter referred to as a standard household questionnaire), while data on proxies would be solicited through a shorter household questionnaire, often with a shorter field implementation period.<sup>3</sup> Even if questions underlying proxy definitions are worded _identically_ across short versus standard household questionnaires, identical questions could yield different answers in questionnaires that exhibit substantial variation in inter- and intra-module scope of data collection.

> 2 Vu and Baulch (2011) evaluate a range of these methods in the context of Vietnam.

> 3 Although the shorter fieldwork for a short household survey would result in cost savings, the differences in the period of implementation between a short household survey and its standard comparator could affect the values obtained for the seasonality-prone poverty proxies. Our set-up ensures that the observed differences between the data obtained from a short vs. standard questionnaire are not due to differences in the period of survey implementation.

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