month period (R1); and (4) a recall-based data collection at the plot-level for a 12-month reference period, administered in a single visit (R2).

The paper provides evidence for the survey practitioners to move away from R2, given the significant underestimation of production and yield estimates, and asserts that the D2 households provided the most accurate information on annual cassava production. The latter is shown to be ensured through sustained participation in diary-keeping, which could have been connected to the relatively more valuable set of in-kind incentives these households received to be part of the experiment – though this hypothesis is not testable. However, as shown in Table 9, D2, while being significantly cheaper compared to the traditional diary operation, it is still more resource- and supervision-intensive compared to the recall variants.<sup>36</sup> The D2 unit cost per household is US$330, compared to US$469 for D1, US$186 for R2, and US$157 for R1.P35F<sup>37</sup> Thus, even if D2 may not always be an option for the survey implementing agencies, it would be more feasible if packaged within a broader effort to collect more frequent data through mobile phone calls on a wider range of topics, including but not limited to extended-harvest crop production, following baseline face-to-face interviews. In the case of Malawi NSO, an effort such as the existing Listening to Malawi (L2M) mobile phone survey, as part of the regional Listening to Africa initiative (Dabalen et al., 2016), could provide such platform. In the worst-case scenario, the analysis indicates that R1 is a second-best alternative to D2 and a clear improvement over R2. R1, at the mean, also performs as well as the traditional diary operation, and comes with less than US$30 additional cost per household compared to R2.P36F<sup>38</sup> On the whole, given the contribution of cassava farming to food security and agricultural commercialization, the evidence underscores the need for adopting improved survey methods to collect better data on cassava production and productivity, facilitating a renewed look at the role of cassava farming in production and welfare outcomes.

> 36 In assessing the CVIP costs by treatment arm, Table 9 breaks differentiates between two broad categories: (1) Fixed costs applied to all treatment arms i.e. training, listing, purchasing of core survey equipment; and (2) Variable costs across the four treatment arms including main fieldwork costs i.e. staff time and fuel; incentives provided to the households; call center set-up and maintenance costs. Furthermore, although CVIP was implemented using the World Bank Survey Solutions CAPI software, the costs of the Android tablets were not considered in Table 9, since these tablets had been readily available at the NSO. Likewise, only maintenance costs were considered regarding the bicycles used by the enumerators and the motorcycles used by the supervisors, as these items too had been available at the NSO.

> 37 The D2 costs were exacerbated, on one hand, by the relatively low number of households requiring semi-weekly calls; the purchase of mobile phones and solar chargers (due to poor electricity access) for all D2 respondents, and were alleviated, on the other hand, given the small number of call center operators and the NSO experience with the Listening to Malawi (L2M) mobile phone survey. In preparation for the CVIP fieldwork, the NSO management worked closely with the two main carriers in Malawi to determine the most cost-effective airtime bundle. An additional cost saving mechanism would have been to provide mobile phones to only those households not currently owning a working device, which may be much more feasible in other settings for low- and middle-income countries.

> 38 For information on how D2 or R1 can be operationalized in the context of existing household survey types in lowand middle-income countries, Moylan et al. (Forthcoming) can be consulted.

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