diaries can complement existing surveys for populations and output categories for which existing recallbased surveys may results in considerable measurement errors.

# **4.1 Comparing diary and recall-based production estimates**

To better appreciate the strengths and potential weaknesses of the diary, it is useful to compare the diary estimates to what has been obtained through recall at the household level via a standard production questionnaire. Table 5 reports the results from comparing the share of respondents who mention having obtained any output from a given crop using each method (columns 1 and 2), the value of that production (columns 3 and 4), and the number of entries in the diary this value corresponds to. We differentiate between cash crops, seasonally or continuously harvested food crops, and fruits and vegetables.

First, for cash crops we find striking differences between diary and recall both in terms of a crop being reported and the actual quantity of output recorded. With the exception of rice, reported quantities for cash crop output and, for coffee and cotton also the incidence of a crop being mentioned, are much lower for the diary than the recall. As this is unlikely to be due to the harvest period falling outside of the window covered by the diary, the most reasonable explanation is that, for this type of remunerative crops, recall may come relatively easy and that a diary, unless properly implemented, may result in underreporting if perceived as being associated with some form of taxation or income monitoring For coffee, 22 percent in the diary, _vis a vis_ 32 percent in the recall survey, mention having any output from the crop and for those who do, reported output is about two thirds lower than for those in the recall (i.e. $ 11 compared to $ 30). The difference in reporting output is more pronounced for cotton (also with a low frequency of harvesting). While sugarcane is mentioned by more households in the diary than the recall (and, with 6.6 entries per reporting household, at a relatively high frequency), reported output is well below the low levels of the recall. In the aggregate, this implies that for cash crops, total output value as reported by the diary amounts to some 56% of what emerges from the recall. While contrary to our initial expectation (according to which error should be lowest for cash crops sales of which are discrete events that are easy to remember, this results suggests that systematic bias in favor of over-reporting of output in the diary is unlikely and that careful empirical study is important.

Second, the match of reported incidence and output values is much closer for most seasonal food crops. In the diaries, reported incidence, which is almost equal for maize and beans, is much higher for field peas and to a lesser extent groundnut (intercropped and thus more likely to be overlooked in the recall survey). Marked differences in terms or harvesting quantity per reporting households also emerge for groundnuts, sorghum, and millet. In some cases, the magnitude of the difference (e.g. $ 125 vs. $ 37) for beans could be due to confusion between fresh and dried produce. At the same time, the comparatively large numbers of entries per reporting household (e.g. 21.5 for beans and 11.4 for maize) highlights that even seasonal 10