6.0
Considering Scales and Comparability
Some basic things should be considered regarding scales when choosing indicators for environmental public health surveillance. To meet program goals, indicators of a variety of different scales will be used, however when aggregating indicators based on geographic scale, one must remember potential loss of detail at smaller scales. Indicators developed with aggregated data (e.g. a specific indicator for health status at the municipal level) may hide inequalities at smaller scales included in the aggregate information (e.g. significant differences between groups of individuals in the municipality). Further, the way in which the information was originally collected (e.g. sample size of surveys) has implications on its ability to accurately represent a specific geographic region or be involved in a valuable aggregated indicator. The ability to compare indicators between and across regions is often an explicit or implicit objective of surveillance and monitoring programs. Comparisons are made to illustrate progress on a relative scale, identify geographical areas requiring greater attention, and often to help orient future goals and objectives. However, the context (political, environmental, economic) in which the indicators are collected must be considered, respected and incorporated for comparisons to be relevant and of value to their purpose or intent. Adjusting indicators to account for such things as economic buying power (for economic indicators such as GDP and income) help to alleviate these problems. Similarly, where differences in standards between two regions exist, individual standards should be retained in comparisons rather than conducting comparisons based on standards of one region. Therefore, in the U.S. – Mexico Border region, we recommend identifying and utilizing local, regional and national standards and procedures of the two countries for components of environmental health (wastes, water, air, etc.) and adjusting, where possible, all economic based indicators for buying power, prior to comparisons between countries.
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