the year for an entire sample, there may be less inequality in the “usual” month measure than in formats with shorter recall periods.<sup>11</sup> Second, the “usual” month format forces respondents to undertake a more difficult cognitive task of _estimation_ , rather than just _memory recall and counting_ required by other modules. There are many estimation strategies that respondents might try when estimating “usual” month consumption, each with their errors. For example, they could estimate monthly quantity from a rule-of-thumb daily consumption rate (“one mango a day during mango season”) and then apply either a lagged price or the current price to convert into consumption values. Or they might estimate monthly spending from mental accounts for shorter periods (“my weekly beer budget is 10,000 shillings, so 43,000 shillings per ‘usual’ month”). What is most unlikely, however, is that they try to remember all occurrences, count them, and then average them.<sup>12</sup> The three diary modules are of the “acquisition type.” Specifically, they add everything that came into the household through harvests, purchases, gifts, and stock reductions and subtract everything that went out of the household through sales, gifts, and stock increases. For example, items that are purchased to be resold, given away, or kept in stock are not counted as consumption. Two modules are household diaries in which a single diary is used to record all household consumption activities. For the third diary module, each adult member keeps their own diary while children were placed on the diaries of the adults who knew most about their daily activities.<sup>13</sup> Following the literature, we label this as a “personal diary.” The personal diary was carefully designed to avoid double counting. Diary entries are specific to an individual and should leave no scope for double-counting purchases or self-produced goods. It is possible that a “gift” could be given to the household and accidentally recorded by two individuals. However, interviewers were trained to cross-check individual diaries for similar items purchased, produced, or gifted that occur on the same day and to query these during the checks. In many cases, one person will 11 For example, Gibson, Rozelle, and Huang (2003) find the Gini coefficient in urban China is 64 percent higher if respondents kept a diary for one month, with the sample spread evenly across the year, compared with the Gini that results from all respondents keeping the diary for one year. In contrast, the annual mean from extrapolating staggered monthly expenditures almost exactly equals the mean from the annual diaries. Since this experiment was carried out in an urban area, the difference is not primarily due to seasonality but instead to short-term fluctuations within the survey period that are subsequently reversed over the year.

12 While the literature has findings about errors in memory and counting (more error the longer the period and the more transactions to count), almost nothing is known about errors in estimation strategies. For example, if respondents apply current market prices to usual month quantities, it reintroduces seasonality into the “usual” month estimate and so will tend to raise inequality toward the level found with short reference periods. In the Vietnam Living Standards Survey, the unit value for rice, formed from the ratio of “usual” month expenditure to “usual” month quantity, has considerable seasonality, with the same pattern across months that is observed in community market price surveys (Gibson, 2007). The community market price surveys reflect current seasonal conditions because they are carried out only once in each cluster but the unit values should not because they are meant to refer to purchases made in a “usual” (that is, an a-seasonal) month.

13 Just over 52 percent of individuals in the respondent households maintained a personal diary, with the remaining members (typically children) allocated to a specific adult personal diary.