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The water portion of the environmental health indicator for developing countries includes a surrogate measure for potential exposure to insect-borne diseases. WRI combined two variables: the number of cases of malaria per country and the country’s total population. The final ranked measure is the percentage of the country’s total population with malaria. Many environmental factors, including fluctuations in temperature, precipitation, and humidity, are linked with the spread of insect-borne diseases. Although many insect-borne diseases have major impacts on human health (e.g., dengue, leishmaniasis, trypanosomiasis, and schistosomiasis), few comprehensive databases exist. Shortcomings aside, malaria data are one of the better data sets available worldwide for an insect-borne disease.
The nutrition portion of the developing country indicator includes three variables that represent potential exposure to poor nutrition: percentage of children younger than 5 years of age who are underweight, total number of available calories per person, and percentage of population at risk of developing either vitamin A or iodine deficiency (whichever micronutrient deficiency was higher). These variables are included to underscore the important correlation between adequate food and nutrition and environmental factors.
Underweight children refers to those younger than age 5 whose weight-for-age is below minus 2 standard deviations (for moderate underweight) or below minus 3 standard deviations (for severe underweight) from the median weight-for-age of the reference population. WRI included the number of calories available per person and populations at risk of developing micronutrient deficiencies as potential measures of an adequate diet. The percentage of the population at risk of developing vitamin A deficiency is estimated by WHO using extrapolations from subnational surveys of the proportion of the total country likely to be affected considering similar ecological conditions. The percentage of the population at risk of developing iodine deficiency is estimated by WHO based on the presence of goiter: persons are considered at risk of developing an iodine deficiency disorder if they reside in a geographical region where the total goiter rate in school-aged children (i.e., children 6 to 11 years of age) is equal to, or greater than, 5 percent. WRI divided WHO’s estimate for the population at risk by the corresponding population data for the country from the U.N. Population Division. <.p>
The three variables within the air, water, and nutrition portions of the developing country indicator were ranked from lowest (lowest relative risk) to highest (highest relative risk). If data were not available for the same number of countries for all of the variables, the ranks of the variables were standardized, or spread, to match the maximum number of ranks for any of the variables within air, water, or nutrition. The three ranks (replaced with a standardized rank when appropriate) were then averaged, and the final average rank was ranked again from lowest to highest risk. To be included in the calculation, each country must have data for at least two variables for air, water, and nutrition.
These calculations were then used to determine a relative rank for the air, water, and nutrition portions of the developing country indicator. The ranks for each portion were then separated into three equal groupings: the first one third represent countries at low relative risk from potential exposure to the environmental health threats, the middle one third represent countries at moderate relative risk of exposure, and the last one third, countries at high relative risk of exposure. Table A.1 shows the low- , medium- , or high-risk scores for each country for each of the air, water, and nutrition portions of the indicator for developing countries.
The next level of aggregation was to combine the ranks of the three portions. Here again, if data were not available for the same number of countries for all of the variables, the ranks of the variables were standardized to match the maximum number of ranks for any of the three portions. The ranks (replaced with a standardized rank when appropriate) were then averaged, and the final average rank was ranked again. To be included in the final ranking, each country had to have data for at least two of the three portions. The final result was a list of developing countries ranked according to potential exposure to the environmental health threats. The final rank was separated into high, medium, and low categories of potential relative risk by dividing the countries into three equal groups.
Developed countries
For developed countries, WRI constructed two variables (or indicators) representing potential exposure to polluted air: potential exposure to polluted ambient air and potential exposure to air polluted with lead from gasoline. These two variables(also used in the developing country indicator discussed previously) were ranked from lowest to highest exposure. The ranks were then separated into three equal categories to represent low- , medium-, and high-relative risk. These ranks were not aggregated as in the developing country indicator, but rather are shown separately in Table A.2.
Refining the indicators
These preliminary indicators are a work in progress that can be improved with additional data. The final rankings for each country are suggestive, not definitive, and should be considered a starting point for exploring environmental health threats in greater detail. Although WRI used the best available data to construct the indicators, data were often incomplete or unreliable. Dividing nations into thirds, to create the three risk categories, is admittedly arbitrary. For instance, there may be very little difference between countries at the cutoff points, between high and medium risk or medium and low risk. The broad categories, however, suggest differences in relative risks, and the indicator maps serve as preliminary tools for identifying countries with different potential for exposure to environmental health threats.