the respondent is presented with a long or a short list of consumption items can influence the quality of the responses.<sup>3</sup>

- _Diary versus recall surveys_ . The consumption diary is the main alternative to the recall approach to consumption measurement. It is generally expected that diaries suffer less from recall or telescoping errors because the consumption is intended to be recorded either simultaneously or soon after it occurs. Of course, this presumed accuracy is only achieved if the diary is used as intended. The extent to which diaries are supervised to ensure they are regularly filled is thus a key design feature. Unsupervised diaries may effectively become self-administered recall modules with endogenous recall periods if some types of respondents do not fill them in every day and, hence, render them subject to varying degrees of recall, telescoping, and rule of thumb reporting. Diaries administered among individuals should also prove better at capturing individual consumption outside the household (i.e. reduced personal leave out error), leading to a higher level of measured household total consumption (Grootaert 1986).

As a net result of these various types of reporting error, consumption estimates based on different methods of data capture (diary versus recall questionnaires), levels of respondent (individual versus household), recall periods, or degree of commodity detail may not be comparable. We have designed the survey experiment used here in part to assess the extent to which variations across these dimensions affects itemspecific and summary consumption measures in relation to the benchmark measure of the daily-supervised individual diary. We chose this diary design, described in more detail in the next section, to minimize the influence of recall, telescoping, personal leave out, and rule of thumb errors.

# **III. The Tanzania survey experiment**

The Tanzania survey experiment, conducted to shed light on the implications of survey design variations in food consumption measurement, systematically contrasts various design features. We strategically selected eight survey designs to reflect the most common methods utilized in low-income countries and that are typical of the scope of variation one is likely to find in consumption surveys. We then randomly assigned these eight designs to over 4,000 total households. Given the sample size and the random assignment of survey designs, differences in mean measurement performance may be attributed with a high degree of confidence to the survey design rather than potential confounders.

The designs differ by method of data capture (diary or recall survey), designated respondent (household head or other household member), length of reference period, number of items in the recall list, and nature of the cognitive task required of the respondents. Table 1 summarizes each of these designs. The modules we number 1–5 are recall designs, and modules 6–8 are diaries. For the food recall modules, households report the value of items consumed from three sources: purchases, home production, and gifts or payments. Modules 1 and 2 contain a list of 58 food items. Module 3 is associated with a subset list that consists of the 17 most important food items, which constitute, on average, 77 percent of food consumption expenditure in Tanzania based on the national Household Budget Survey 2000–01. To make module 3 comparable, we scale up reported expenditures for that module (by 1/0.77). Module 4 is associated with a list of 11 food items. It is an aggregated version of the list of 58 food items whereby, for example, several

> 3 Beegle et al. (2012) find a drop from 49 to 41 minutes in interview times if the food list is cut from 58 to 17 items in a one-week recall. Times for a 58-item list rise to 76 minutes if the typical, more cognitively demanding “usual” month recall is used.

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