Root for the tubers: Extended-harvest crop production and productivity measurement in surveys

Root and tuber crops, such as cassava, could be planted to hedge against climate shocks, seasonal crop failures and food insecurity during the lean season. Since their harvests occur over extended periods and often in small quantities, they present a serious challenge for household and farm surveys aiming to collect reliable information on crop production based on recall. To document the relative accuracy of recall-based approaches to survey data collection on cassava production vis-à-vis diary-based techniques, a survey experiment was implemented in Malawi over a 12-month period. The sampled cassava-producing households were randomly assigned to one of four treatments, including (1) daily diary-keeping, with semi-weekly supervision visits (diary-visit); (2) daily diary-keeping, with semi-weekly supervisory phone calls (diary-phone); (3) two six-month recall interviews, with six months in between; and (4) a single 12-month recall interview. We find that compared to diary-visit, the household-level annual cassava production is 295 kg higher under diary-phone. This effect corresponds to 28 percent of the average diary-visit annual production estimate. Since unavoidable, albeit limited, lapses in diary keeping over a 12-month period may have led both diary variants to underestimate true production, higher annual cassava production estimate obtained under diary-phone implies that this treatment is closer to the true estimate. Although the difference between the estimates based on six-month recall and diary-visit is statistically insignificant, 12-month recall, on average, underestimates annual production (i) by 516 kg with respect to diary-phone (corresponding to 37 percent of the diary-phone average) and (ii) by 221 kg with respect to diary-visit (corresponding to 21 percent of the diary-visit average). While the recall-based approaches both record production estimates lower than the diary-phone, six-month recall does so to a lesser extent. And supported by a crop cutting operation in which all sampled households participated irrespective of their assigned survey treatment, the analysis demonstrates likely gross overestimation in competing international and ministerial statistics on cassava yields in Malawi. For improved microdata on root and tuber crop production, the findings lend support to the adoption of (i) diary-keeping with phone calls, particularly if deployed in a broader mobile phone–based survey, or (ii) six-month recall, as a second-best alternative. The adoption of these practices can then facilitate a renewed look at the role of cassava farming in poverty, food security and agricultural production.