question excludes telescoping as the cause, it is likely that the rules of thumb used by respondents underlie the misreports. We provide further evidence of this below by showing that the overestimates are worse for infrequently purchased items. Finally, the consistent shortfall in incidence in the two household diaries with respect to the personal diary points to the importance of personal leave out error because this is the main driver of divergence between modules 6 and 7 and the benchmark.

Key household characteristics may exacerbate (or moderate) the module-specific reporting error in consumption incidence. This can be explored by interacting the module indicator with the select characteristics mentioned earlier Table 4 summarizes these results by reporting the food groups on which significant interaction effects have been estimated.<sup>13</sup> The effect of household characteristics on the incidence reported not only depends on the characteristics, but also on the particular food subgroup. For recall modules in general, the tendency to underreport incidence is mediated by urban location, the education of the household head, and household wealth, at least for numerous key food groups such as Cereals, Sugars, and Meat and Fish. (This is because, while the module effect is negative, most of the interaction terms are positive.) Thus, the underreporting of any consumption in these food groups is greatest among rural, less well educated, and low-wealth households. For some food groups, the number of household members, especially the number of children, also tends to exacerbate underreporting. This implies that more disadvantaged households, those that are rural, have less education, have more children, and have fewer assets are more likely to omit consumption during the survey experience. This will exaggerate their monetary poverty status. These households may especially benefit from increased enumerator attention and explicit prompting for consumption incidence on a good-by-good basis.

In contrast, the household diaries seldom have significant interactions with household characteristics, suggesting that the downward bias in consumption incidence in these modules is fairly constant across all households. Exceptions to this include the consumption incidence of Fruit, Pulses, and Nuts/Seeds recorded among urban households, where the reported incidence of these groups is significantly lower. This implies that the individual consumption of select food groups is more likely to be missed in urban households with diaries than rural ones; perhaps these items are even more commonly eaten outside the home in urban areas than in rural areas.

# _Survey design and the value of consumption_

The same analytic framework used for the analysis of relative consumption incidence is applied to reports of consumption value (conditional on positive consumption) in Tanzania shillings.<sup>14</sup> Table 5 summarizes the module design effects of the reported consumption values, all converted to monthly equivalents. Differential reporting behavior by module type is clear. The 7-day recall records significantly higher consumption values for most food groups; the four exceptions are Tubers, Vegetables, Meat and Fish, and Oils/Fats, for which the quantities reported are not different than the benchmark. Because these goods are typically more perishable than other types and, consequently, purchased more frequently, perhaps the tendency to overreport consumption value is mitigated by these characteristics. In contrast, the 14-day recall values are all lower than the 7-day recall values and generally exhibit negative value errors. Only in the

> 13 The specific interaction terms are presented in appendix table 2. The main effects estimated in equation (3) are suppressed for ease of exposition.

> 14 The monetary value results can also be interpreted as the effect on reporting quantities (kilograms or liters).

11