6 us a person’s individual location as well as their income (or consumption) in each period. Then we could, in effect, decompose national poverty change into the poverty effects of (i) income growth in rural areas, small towns, and cities, i.e. income growth among those who stayed in each of these three areas, and (ii) income changes as the result of (net) migration across these categories, i.e. income growth among those who moved from rural areas to small towns, from rural areas to the city, from small towns to the city and vice versa.<sup>5</sup> Christiaensen, Kaminski, Sim and Wang (2017) do so using the National Panel Survey of Tanzania (2008‐2012) (Table 1).<sup>6,7</sup> Overall, poverty did not decline much over this period (by 0.42 percentage points), consistent with the low annual growth in consumption (1.16 percent). Yet, these averages hide a lot of heterogeneity especially between non‐movers and movers and depending on the destination (rural, town, city).<sup>8</sup> The vast majority of the population (91 percent) did not move and experienced very little consumption<sup>9</sup> growth or poverty reduction. Among them, poverty reduction was largest among those who stayed in secondary towns. Among city dwellers, growth was even slightly negative and the poverty headcount increased slightly.

These relatively small changes in (average) welfare contrast with the changes observed among the movers. Their poverty declined by 5.8 percentage points (and their average annual consumption growth amounted to 8.35 percent). More strikingly, income growth and poverty decline were especially substantial among rural‐urban migrants, while moves back to the rural areas (from the town or the city) came along with a substantial increase in poverty incidence (from 4.5 to 14.8 percent and from 0 to 13.1 percent respectively). Urban‐rural migration did not necessarily result in a decline of average income growth though. Return migration does not signify failure for everyone (Hirvonen and Lilleor, 2015) .

Looking within the urban space, rural‐town migration contributed most to overall poverty reduction (twice as much as rural‐city migration, 105 percent versus 49 percent respectively), even though rural‐city migration contributed more to overall income growth. The reason for the larger contribution to poverty reduction by rural‐town migration follows from the fact that 4 years later about twice as many rural citizens were found in a secondary town than in the cities (3.4 percent versus 1.7 percent), while the decline in poverty incidence among both groups was very similar (13.1 and 12.4 percentage points respectively). When it comes to income growth however, rural‐city movers saw their incomes grow much more than those moving to towns, overcompensating for the fact that only half as many ended up in the city.

These findings draw attention to the critical role secondary towns appear to have played in poverty reduction in Tanzania. This follows, at least in an accounting sense, from the fact that many more rural dwellers (including poor rural dwellers) ended up in towns, even though the income gains among those who were found in the city, were much larger. Yet, those making their way to the city might have

> 5 Christiaensen, De Weerdt and Kanbur (2018) elaborate the technical basis for these decompositions.

> 6 Among those who stay in rural areas, they further split off those who go to a rural area in another region. 7 The authors abstract from statistical weight adjustments for differential natural population growth rates across space.

> 8 In their decomposition, urban centers with more than 500,000 inhabitants are classified as cities. They consist of Dar es Salaam and Mwanza (capital of the Mwanza region), with an estimated population of 4.36 million and 0.7 million people, respectively, as of 2012.

> 9 Consumption and income will be used interchangeably.