diary, effectively blurring the line between consumption data collected by diary and by recall interview. This mediation by interviewers is especially likely since most diary surveys instruct interviewers to return every few days to update the diary in cases where it may not be completed by household members, such as in households with no literate adults.

While well-implemented diary surveys might be expected to yield higher (and presumably closer to actual) levels of consumption, experimental evidence for this from developing countries is fragmentary. In urban Papua New Guinea, Gibson (1999) found that mean total expenditure per capita was 14 percent higher (and food consumption 26 percent higher) using a diary rather than a recall survey. However, preliminary comparisons of consumption from the Bosnia and Herzegovina LSMS (recall) survey with the household budget survey (diary) in 2004 show levels to be similar (World Bank, 2006).

These studies pertain to household-level diaries and thus do not address an important source of mis-measurement – the difficulty of a sole respondent to perfectly capture total household consumption. Personal diaries are generally considered better for obtaining complete household expenditure or consumption data because it is unusual, in most societies, for any one household member to know the expenditure/consumption of every other member, especially on items such as alcohol, tobacco, daily travel, personal toiletries, daily newspapers/magazines, and meals (especially snacks and lunches) eaten outside the home. In Russia, as part of an effort to study the reliability of the Household Budget Survey, a random sample of households in the 3<sup>rd</sup> quarter of 2003 were assigned personal diaries rather than the household diary. The personal diary yielded expenditure levels which were 6-11 percent higher than a household diary (World Bank, 2005). However, the personal diary was plagued with non-respondent problems in this experiment; about 54 percent of households assigned the personal diary did not complete it. Personal diaries also create the possibility of inadvertent double-counting of items consumed in common but reported separately by two or more individuals, and so care must be taken with this method. We discuss this further in the next section.

While the perfect diary experiment is, essentially, the benchmark for collecting consumption data through survey, it is difficult to extrapolate from experiments between diary and recall consumption modules if the implementation of the diary in the experiment does not reflect the reality of fielding a diary in developing or transition countries. It may be that in the case of illiterate (or simply unmotivated) respondents, a 7-day diary becomes a 7-day recall survey if the information has to be obtained orally by the interviewer at the end of the period. The implications of variation in literacy, motivation, and other factors, although not well-documented, implies that it can be quite difficult to conduct a high-quality diary survey, regardless of issues related to respondent recall bias.

In their study of measurement errors in food consumption, Ahmed et al. (2006) observe problems in the Canadian Food Expenditure Survey diary related to infrequency and diary exhaustion and conclude