First, we create _nutritional value weights_ for each COICOP group. We take the average nutritional score across food items for each COICOP group. To generate the group weights, the COICOP group scores are normalized so that they sum to one. Second, we create an _unweighted price index_ for each COICOP group. We take the average of the item-wise indexes within a given COICOP group to generate a COICOP group index.<sup>17</sup> Third, for each time point, we calculate the NPI or the _weighted average_ price index across COICOP groups, using as weights the nutritional value weight for each group. Note that the NPI reflects the change in food price based on nutritional value, unrelated to actual purchasing behaviors. It is thus a normative measure (based on what is most nutrient-dense) rather than a descriptive one (what people actually consume).<sup>18</sup>

# **4 Results and discussion**

# 4.1 The varying cost of a recommended diet across geographic location

We calculate the cost of a CoRD-based nutritious diet (daily cost per individual per day) using food price data from Sri Lanka for December 2017, from Pakistan for June 2017, and from Afghanistan for September 2017. For these respective months in 2017, the cost of such a diet was SL Rs 187 ($2.05 in 2011 $PPP) in Sri Lanka, 87 Prs ($1.43 in 2011 $PPP) in Pakistan, and 45 Af in Afghanistan.<sup>19</sup> We caution against comparing these values across countries because the costs were measured during different months. Our CoRD estimates suggest that the cost of food might be more prohibitive than other calculations show. Back-of-the-envelope calculations suggest that the cost of a CoRD-based diet is higher than that for the official (calorie-based) food component of the official poverty line. Specifically, it was higher than the cost of the food component of the poverty line by 38 percent in Sri Lanka and by 15 percent in Afghanistan.<sup>20</sup> We caution, however, that for Sri Lanka, the data is from December 2017 which tends to have a higher price level. In any case, this indicates that policymakers may be underestimating the cost of basic food needs if we instead consider food-based dietary guidelines as a benchmark diet. The CoRD estimate is important because FBDGs constitute official government guidance, suggesting diets that all people should consume, and nutrition education programs are often based on such guidelines.

<mark>The lowest-cost foods in each group will vary by season; the foods selected using our specific data provide a snapshot of the composition of the recommended diet. In Sri Lanka, the lowest-cost items (per serving edible portion, December 2017) for starchy staples were white rice and red rice; for protein foods, red lentils (red dal) and soya beans; for dairy, fresh cow milk and condensed</mark>

> 17 If item-wise indexes are unavailable, but item-wise prices are, then we calculate the indexes by taking the percent difference in the price of the item in a given month-year with the price in the base month-year, and then adding 100.

> 18 For Afghanistan, the price indexes are only available for COICOP groups and not for each individual food item. Such price indexes already reflect the expenditure weights for each food item within a COICOP group. While we can calculate some version of the NPI using these price indexes, the resulting NPI will not be purely normative as the price indexes implicitly integrate expenditure weights into their calculation. In effect, such an NPI would be a hybrid of the standard CPI and the NPI, combining a normative and descriptive measure, making it less intuitively interpreted.

> 19 For Sri Lanka and Pakistan, we use the 2011 PPP$ conversion factor specific for food and nonalcoholic beverages. The PPP$ conversion factor is unavailable for Afghanistan.

> 20 In Sri Lanka, the food component of the poverty line (using a nutritional anchor of 2,030 calories) was valued at 128 rupees per person per day in 2016. We inflate this using the Colombo CPI (6.6 percent increase in December 2017) to get 136 rupees per person per day in December 2017. In Afghanistan, the food component of the poverty (using a nutritional anchor of 2,100 calories) was valued at 23 afghanis per person per day in 2007. We inflate this using the national CPI (with base in April 2015, suggesting an increase of 1.7 times between September 2007 to September 2017) to get 39 afghanis per person per day in September 2017. Note, however, that the cost of basic food needs is lower than the calories included in the recommended diet.

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