A critical appraisal of environmental indices

Abstract

In response to growing concern about human-induced environmental degradation, a number of countries have produced "state of the environment" reports (SERs). These reports typically contain data from a large number of environmental variables. This raises the question of how best to report these large quantities of data. One approach is to integrate the raw data into some form of composite index, thus reducing its volume. Critics of this approach suggest that so much information is lost in the process of producing the index, that the final result is at best of little use, and at worst misleading. This study attempts to determine whether it is possible to construct a useful index of environmental quality, either for the whole environment or for a specific compartment such as air, water, or soil.

The study also presents the following: a new method for classifying environmental indices; a framework for assessing the usefulness of these indices; and preferred definitions of a number of terms in the field of environmental management.

Two examples of overall environmental quality are described, and their 'usefulness' is assessed in terms of three criteria: their completeness, plausibility, and the extent to which they could help the public in deciding whether to support proposed environmental policies. The two indices described do not meet all these criteria. It is concluded that it is not possible to construct an overall environmental index that does meet these criteria.

Various published indices of air, water, and soil quality are then described in turn, and each is assessed for "usefulness" using the above criteria. It is concluded that it is not possible to construct such indices to meet these criteria, due to difficulties in assigning weightings to the numerous variables involved, and in resolving different interpretations of "quality". It is recommended that individual variables be reported, rather than any composite index, when future SERs are compiled. In addition, a summary is given of the way in which air, water, and soil quality is reported in various "state of the environment" reports (SERs). It is noted that most SERs report on the levels of individual contaminants, rather than a composite index.

The large number of hazardous air pollutants makes it impractical to report concentrations of individual pollutants. Four types of hazard index are described, ranging from simply reporting the total mass of pollutants emitted, to combining modelled environmental concentrations of chemicals with human toxicity data. Some drawbacks of each method are noted, and a method for comparing the data requirements of any hazard index is presented.