The 2015 release of the Natural Resource Protection Indicator (NRPI) and the Child Health Indicator (CHI) are computed as a standardized proximity-to-target ranging from 0 (worst performance) to 100 (at target or best performance). For Access to Adequate Sanitation and Access to Improved Water, the proximity-to-target measure is equal to the reported percentage. For example, if a country has 84% of its population with access to adequate sanitation, it is considered to have a proximity-to-target score of 84. For child mortality, we compute the ratio of the measured probability of dying to the highest observed probability of dying, which in 2010 was 0.141, and multiply that by 100 to make it comparable to the 0-100 scale used in the other measures. The proximity-to-target measure is this number, which ranges from 0-100, subtracted from 100. For example, a country whose children in the 1-5 age group have a probability of dying of 0.004 would have a proximity-to-target score of 97.2 (0.004/0.1414 = 0.028; 0.028 x100 = 2.8; 100-2.8 = 97.2). The Child Health Indicator is the simple average of the three proximity-to-target scores for water, sanitation, and child mortality.
For Natural Resource Protection, all scores by biome are capped at 17%, which is the target established at the 10th Conference of Parties of the Convention on Biological Diversity (Nagoya, Japan). The scores are capped so that greater than 17% protection in a given biome does not offset less than 17% protection in another biome. Since the range of protection levels across all countries is from 0-17%, the proximity to target scores is then calculated as the ratio of the weighted biome protection percentage to 17%, multiplied by 100. Thus, a country with 5% weighted biome protection would be calculated as follows: 5/17 = 0.29411; 0.29411 x 100 = 29.41.
Note that if values are missing for either water or sanitation (but not both), it is assumed that the score for the missing value is the same as the one that is available and the score for the missing value is imputed from the one that is available. The water and sanitation access estimates are published every two years. We use earlier values where available to fill in gaps so that countries are not penalized for not having up-to-date estimates. However this gap filling with earlier data is only performed when both water and sanitation measures are available for the earlier time periods, and not when a country is missing one of the two.