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Multimetric Indices to Prepare and Analyze Data

Multimetric Index

An index that combines indicators, or metrics, into a single index value. Each metric is tested and calibrated to a scale and transformed into a unitless score prior to being agreggated into a multi-metric index. Both the index, and metrics, are useful in assessing and diagnosing ecological condition. Different approaches have been used to prepare and analyze biological indicator data.  But they all start out with a list of aquatic life that was collected and identified.  This list  is often called a "species" list, but because many benthos can not be identified to species, it is also called a "taxon" list.

In the past, the presence or absence of a few indicator species, such as game fish, was used to assess watershed health.  But scientists realized that the assessment was a little more complicated than just using indicator species.   Eventually, length and weight measurements of fish were also used, and numeric indices for benthos were developed. Such indices were first called biotic indices because they assigned number scores to the pollution tolerance of many different biological indicator species.  While biotic indices were expanding in use, other indices, such as diversity indices, grew in popularity and were used for many years.

Recently, multiple metric indices, such as the Index of Biotic Integrity by Dr. James Karr (1981), have become the standard in the United States for accurately assessing watershed health. Five activities are central to making multimetric biological indexes effective:

  1. Classifying environments to define homogeneous sets within or across ecoregions (e.g., streams, lakes, or wetlands; large or small streams; warm-water or cold-water lakes; high- or low-gradient streams).

  2. Selecting measurable attributes that provide reliable and relevant signals about the biological effects of human activities.

  3. Developing sampling protocols and designs that ensure that those biological attributes are measured accurately and precisely.

  4. Devising analytical procedures to extract and understand relevant patterns in those data.

  5. Communicating the results to citizens and policymakers so that all concerned communities can contribute to environmental policy.

For even more information, take a look at Developing Metrics and Indexes of Biological Integrity (PDF, 1.5 MB) from EPA's Web page on Methods for Evaluating Wetland Condition. Much of the information presented on this page is taken from "Restoring Life in Running Waters" by James R. Karr Exit EPA Disclaimer and Ellen W. Chu Exit EPA Disclaimer (1999, Reprinted with permission from Island Press).

For more information:

 

Biological Indicators | Aquatic Biodiversity | Statistical Primer

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