Nigeria suffered from slow growth and a series of shocks, even before the arrival of the COVID-19 crisis. Nigeria has consistently been affected by climate shocks, especially for farmers relying on rain-fed agriculture and livestock herders, as well as conflict, especially for communities in the north of the country, for several decades. In 2016, the collapse of global oil prices pushed Nigeria into recession, with real GDP dropping by 1.6 percent, given Nigeria’s continued dependence on oil: fuel has made up more than 80 percent of exports since the 1970s. Growth remained subdued during the 2017-2019 period, below the growth rate of peer economies and the rate of population growth, resulting in a steady decline in per capita incomes. The onset of the COVID-19 pandemic and the corresponding drop in global oil prices has only weakened Nigeria’s macroeconomy further, with real GDP dropping 1.8 percent in 2020.

Despite Nigeria’s size and its importance for regional and global poverty reduction, the infrequent availability of survey data on household welfare makes it difficult to track how poverty evolved in the country in the decade before the COVID-19 crisis. The two most recent official household surveys used for poverty measurement, the 2009/10 HNLSS and the 2018/19 NLSS, capture household consumption very differently and therefore produce incomparable poverty estimates. In particular, the module used to collect information on food consumption was changed from a daily diary, handed to enumerators during four visits over the course of one month, in the 2009/10 HNLSS, to a seven-day recall, in the 2018/19 NLSS. Additionally, the approaches for measuring meals outside the home and own-produced food were changed between the two surveys. Key non-monetary variables were also collected differently in the 2009/10 HNLSS. Evidence suggests that changes to the survey questions used to capture consumption can alter poverty estimates considerably (Deaton 2005, Beegle at al. 2012). The poverty headcount rate estimated using the 2009/10 HNLSS is 56.4 percent. Given these differences, it would be erroneous to compare this estimate with the latest poverty headcount rate of 39.1 percent estimated using data from the 2018/19 NLSS.<sup>4,5</sup> This paper explores other analytic solutions to fill this gap and finds alternative methods to estimate a long-run poverty trend in Nigeria.

> 4 Beyond changes in the consumption module, the data collection for the 2018/19 NLSS has substantially improved compared to previous years (detailed survey documentation can be found in the World Bank Microdata Library available here: https://microdata.worldbank.org/index.php/catalog/3827/related-materials). Among other improvements, the 2018/19 NLSS switched to CAPI allowing for better real-time monitoring of data collection. 5 The regional and global poverty estimates currently published by the World Bank are based on an interpolated poverty trend between these two estimates for Nigeria. In effect, this trend erroneously compares the two estimates and results in estimating a drop of around 17 percentage points in Nigeria over the decade between 2009 and 2019. The evidence presented in this paper unveils a much lower reduction in poverty and stresses the importance of collecting frequent and comparable data when measuring poverty over time.

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