adjustment for inter‐year price variations. Most of these differences affect the food line and are explained more in detail below.

# **i. Food line**

Both the NPS 2010/11 and the HBS 2011/12 poverty lines are based on a food basket concept and correspondingly anchored in nutrition. The HBS 2011/12 food poverty line (TZS 26,085.5 per adult per month) is based on the cost of a food basket that delivers 2,200 calories per adult per day. The cost of buying 2,200 calories is derived from the food consumption patterns prevailing in a reference population—the 2<sup>nd</sup> to 5<sup>th</sup> decile of the distribution of total consumption per adult equivalent. Consumed quantities are converted into calories using the NBS’s calorie conversion factors and valued at national median prices (the same as the reference for the Fisher deflators).<sup>10</sup> The NPS 2010/11 food line (TZS 18,718.7 per adult per 28 days) is based on a similar concept as the HBS, but differs from the latter in the following respects: 1) the reference period: the food line is based on real consumption per adult equivalent per 28 days while in the HBS it is based on 30.4 days; 2) the reference population group: the reference population is the whole population below the median of total household consumption per adult equivalent;<sup>11</sup> and 3) the method of evaluation of the cost per calorie: NPS uses the median prices paid by the reference group instead of median national prices to evaluate the food line.<sup>12</sup> 10 The food line in the HBS 2011/12 is estimated as follows: where _qk_ is the total quantity of item _k_ consumed in the reference population, _p0k_ is the national median price of item _k_ , _qhk_ is the quantity of item _k_ consumed by household _h_ , and _calk_ is the corresponding caloric conversion factor of each item established by the Tanzania National Bureau of Statistics. Median prices _p0k_ are based on the most frequent unit of consumption for each item, with all units being converted to the most frequent unit when possible. If the household consumed the food item in a unit that does not have a metric conversion to the most frequent unit (e.g. piece to kg) the respective item is dropped.

> 11 The reference group in the NPS includes the bottom 50 percent of the population ranked in terms of _real_ per adult equivalent consumption as opposed to nominal per adult equivalent consumption. Real consumption is obtained by adjusting the nominal consumption according to temporal and spatial cost‐of‐living differences. Temporal price differences are associated with seasonal differences (quarters), while spatial differences are associated with the location of a household (geographic stratum: Dar es Salaam, other urban, rural, Zanzibar). Consequently, households with the same level of nominal consumption per adult equivalent might have different levels of real consumption if they face different costs of living.

> 12 NPS daily food line� ∑��∙�����∑�� ��∙���⁄� ∙ 2,200; where _pk_ is the median price of item _k_ in the reference population, ��� is the _average_ per adult equivalent consumption of item _k_ , and ��∙����� �∑�� ������ is the total caloric consumption per adult equivalent by household.

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