# **I. Introduction**

Bangladesh has consistently implemented the Household Income and Expenditure Survey (HIES) every approximately five years since 2000. Before HIES, the Bangladesh Bureau of Statistics (BBS) monitored poverty using a smaller survey limited to collecting expenditure data (Household Expenditure Survey, HES). Four HIES rounds were collected until 2016/17 under the same survey design, data collection processes with no changes in critical questionnaires, like the food and non-food consumption modules, recall periods, and data entry and management (i.e., Pen-and-Paper Personal Interview (PAPI) and Computer Assisted Field-Based Data Entry (CAFE)).<sup>3</sup> Nevertheless, despite maintaining these aspects unchanged, comparability over time was not always fully guaranteed. For instance, the 2016/17 HIES introduced vital changes that could have affected its comparability with previous rounds. Notably, the sample size increased significantly from 12,240 households in 2010 to 46,080 in 2016, enhancing the survey's granularity for poverty estimates at various administrative levels. This expansion necessitated shifting the sampling frame from the Integrated Multiple-Purpose Sample to Enumeration Areas from the 2011 Population and Housing Census. This shift impacted the survey strata and increased the coverage of urban slum areas. Additionally, changes in geographic classifications and the replacement of Statistical Metropolitan Areas with a new Rural/Urban/City Corporation classification affected urban comparability. The larger sample size and revised fieldwork protocols led to more incomplete and inconsistent income data, particularly for wealthier rural households. Despite these issues, the changes are not deemed to significantly alter the overall findings of the poverty assessment (World Bank, 2019).

In the 2022 HIES round, Bangladesh implemented survey design and fieldwork operation improvements that impacted consumption comparability over time.<sup>4</sup> Introducing the Classification of Individual Consumption According to Purpose (i.e., COICOP) increased the number of food and non-food items from 149 to 263 and 261 to 441, respectively. The data collection method moved from PAPI to Computer Assisted Personal Interviewing (CAPI). Market prices were collected instead of deriving unit values from collected household total expenditure values and quantities, and weighing scales were implemented to ensure the accuracy of household consumed food items. A more rigorous fieldwork monitoring system

> 3 To mention a few examples, the 2010 HIES round redesigned the Remittances and Migration modules, and in the 2016/17 round, the Social Safety Net questionnaire was redesigned and expanded. Another difference between survey rounds is that the PSUs in all rounds but 2016/17 were selected from an Integrated Multipurpose Sample (IMPS) – a master sample updated for each Housing and Population Census. In the 2016/17 round, PSUs came from a list of Enumeration Areas used for the 2011 Population and Housing Census. For further details, see Ahmed et al. (2019).

> 4 As technology and survey design methods evolve, enhancements should be implemented. For instance, Argentina improved its survey instrument and periodicity of data collection in 2003, India made several changes in the late 1990s, Peru and Ecuador made significant changes in their household surveys in 2004 and 2007, and, more recently, Zambia and Bhutan in their 2022 survey round. In the ideal situation, a proper way to implement these changes is to simultaneously conduct old and new methods and then clearly identify their differences to maintain comparability over time. However, this process could be costly, challenging, and complex, leaving most countries with two options: break trends or find an analytical way to tackle this issue after implementing the survey.

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