The Survey of Household Welfare and Labour in Tanzania (SHWALITA) survey experiment entailed fielding eight alternative consumption questionnaires randomly assigned to 4,000 households in Tanzania. The eight designs vary by method of data capture, level of respondent, length of reference period, number of items in the recall list, and nature of the cognitive task required of the respondent. Modules 1-5 are recall designs and modules 6-8 are diaries. These eight designs were strategically selected to reflect the most common methods utilized. The alternative designs focus on variation in the measurement of food consumption and expenditure on select frequently purchased non-food items, and not on general non-food expenditure where, due to the infrequency of purchase, there is a much greater degree of design harmonization in practice. Food consumption includes the quantity consumed from three sources (purchases, home production, and gifts/payments) and, for purchases only, the corresponding value of the quantity (in Tanzania shillings). Modules 1 and 2 seek the consumption values for a long list of 58 commodities. In module 3, the subset list consists of the 17 most important food items that constitute, on average, 77 percent of food consumption expenditure in Tanzania based on the previous Household Budget Survey. When comparing consumption expenditure in module 3 with other modules, we scale up food expenditures for that module (by 1/0.77), as is commonly done in practice. Module 4 is a collapsed list where the 58 food items are aggregated into 11 comprehensive categories. Since respondents often use local units for reporting, the survey teams also established conversion factors for these local units and surveyed local prices so that quantity and value information in diaries could be checked for outliers
Among the recall modules, module 5 deviates from a reporting of actual expenditure over a specified time period. Instead it asks for “usual” consumption, following a recommendation in Deaton and Grosh (2000), where households report the number of months in which the food item is usually consumed by the household, the quantity usually consumed, and usual expenditure in those months. These questions aim to measure permanent rather than transitory living standards, without interviewing the same households repeatedly throughout the year. Hence, module 5 introduces two key differences from the other recall modules: a longer time frame and a different cognitive task required of respondents.
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. 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. 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 acquire food for the household (such as buying 5 kilograms of rice), which is entered in the diary of the person acquiring the food. So the personal diary is a not an individual’s record of food consumption. Rather, it records the food brought into the household by each member even if for several members to consume (as well as food consumed outside the household). This intensive supervision of the personal diary sample would be impractical for most surveys but these investments were made in order to establish a benchmark for analytic comparisons.
Each of the eight designs varies how food expenditures (including value of home production and consumption) are collected. Non-food items are divided into two groups based on frequency of purchase. Frequently purchased items (charcoal, firewood, kerosene/paraffin, matches, candles, lighters, laundry soap, toilet soap, cigarettes, tobacco, cell phone and internet, and transport) were collected by 14-day recall for modules 1-5 and in the 14-day diary for modules 6-8. Non-frequent non-food items (utilities, durables, clothing, health, education, contributions, and other; housing is excluded) are collected by recall identically across all modules at the end of the interview (and at the end of the two-week period for the diaries) and over the identical one or 12-month reference period, depending on the item in question. Any cross-module differences in measured non-frequent non-food consumption we take as due to spillovers from the different amount of memory training or conditioning of respondents that may be induced by the different food consumption modules.