Best and Worst Quintiles
Abstract
The Quintile method maps the watersheds in the best and worst environmental condition. A watershed's color is based on how many of its variables fall into the best 20% or worst 20% (emphasizing the top and bottom quintile) of the range for that variable across the region. This creates maps that separate high quality areas from poor quality areas.
Method Details
For the Quintile analysis, the range of each variable is divided into 5 equal intervals. Each watershed is then evaluated in terms of the number of its variables that fell into the best or worst quintiles. The watersheds were depicted using the best quintile scores divided into seven equal intervals and then again using the worst quintile scores divided into seven equal intervals. Only the three best or worst septiles are displayed on the maps.
Limitations
The Quintile method does not account for correlation between environmental measures. Therefore, if several variables measure forest condition in slightly different ways, a watershed with intact forest will have high scores for many variables and therefore have a high best-quintile score. Any assessment based on this method should be done with caution and only accepted if supported with confirming independent evidence. Because this method provides a quick overview of the region, it is best used for preliminary visualization.
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