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Water: Recovery Potential

Step 5: Compare Your Waters


The calculations in step 4 enable you to use the screening run results in step 5 by comparing the relative recovery potential of your waters. Again, there is considerable flexibility in how to use your data to make these comparisons. Three basic approaches are briefly described here: rank-ordering, three-dimensional bubble plotting and mapping. All three of these basic comparison methods are useful, although their strengths differ as noted below. Each takes relatively little effort to generate and can offer strikingly different insights into recovery potential differences among different waters. The purpose of step 5 is not yet to reach final decisions, but to build insights from your screening results through different methods of comparison and visualizing. As such, you can think of the techniques below as 'discussion support' tools rather than 'decision support' tools - each offers a way to organize complex information, stimulate insights about differences, and reveal alternatives for action rather than prescribe a single decision.

Rank-ordering. The simplest of comparison methods, rank-ordering organizes screened waters from highest to lowest recovery potential based on their scores. This is an easy and transparent method to identify a subset of more restorable waters, whether by selecting a specific number or a percentage of highly-ranked waters in consideration of available restoration resources and capacity. The appeal of rank-ordering is its clarity and simplicity - some waters or watersheds simply score higher than others - which may help users move past overly complex discussions without decision criteria.

The flexibility in rank-ordering is in which scores to use. The RPI score described in step 4 is one option for a single overall score used to rank-order all the waters based on all the indicators measured. In addition, each of the three summary indices are easy to rank-order to compare scores on a purely ecological, stressor, or social basis. It is also possible to examine the rank-ordering of a single indicator, if sufficiently important. It is crucial to remember that, if the stressor index is used for rank-ordering, the lowest scores are rank-ordered as the highest recovery potential. For the ecological and social indices and the RPI score, the highest scores are associated with the highest recovery potential.

Although rank-ordering is useful in distinguishing major differences between very high and very low watershed scores, most data likely to be used in a screening probably does not support assuming that very small scoring differences are significant. For example, the 237th-ranked watershed probably is not clearly less restorable than the 236th-ranked watershed. Users are advised not to overemphasize the significance of very small rank-order differences. One option for further organizing rank-ordered lists in a more generalized ranking is to group them by quantiles, which can be equal-size or separated by natural breaks in the range of values. See also ways to use rank-ordering (PDF) (4 pp, 727K, About PDF) in Recovery Potential Screening.

Three-dimensional bubble plotting. This comparison method was adapted specifically for Recovery Potential Screening as a way to visualize the relative influence of ecological, stressor and social context factors on restorability at the same time. Unlike rank-ordering's simplicity, bubble plotting acknowledges that comparisons are often complex and offers a systematic way to observe and consider the relative influence of three major driving factors on restorability simultaneously.

The plotting method runs data from the recovery potential data table through a 3D plotting script written in the open-source R statistical program Link to EPA's External Link Disclaimer, which is used internationally in a wide variety of scientific activities. The three-dimensional approach enables the user to see the ranges and relative differences among the screened waters for all three summary indices at one time. A 3D plot displays screening results as waters plotted relative to X (stressor index) and Y (ecological index) axes, with dot size varying with social context index score. For example, this type of display might enable a user to identify those waters that have high ecological and low stressor summary indices by where they fall on the plot, and then further sharpen their focus on those that have larger dots implying higher social scores. See the 3D plotting example (PDF) (8 pp, 594K, About PDF) for a more detailed description of using the plotting script, and ways to use bubble plotting (PDF) (6 pp, 619K, About PDF) in Recovery Potential Screening for a discussion of how this technique can aid comparison and targeting decisions.

Mapping recovery potential screening results. Mapping is a universally familiar and popular method for displaying comparative environmental information. The variety of available mapping options created in recent years through advances in GIS technology goes far beyond the scope of this website. Like the other two techniques, mapping has strengths and weaknesses relative to Recovery Potential Screening.

Because many recovery potential indicators come from GIS data, and screening is organized around a data table with each record referenced geographically to a specific water or watershed ID, virtually all of the data outputs from screening can be displayed in map form. The overall RPI score, for example, can be displayed for a statewide set of watersheds by assigning a light-to-dark color range that corresponds to the high-to-low RPI score gradient. Similar maps could be developed for the ecological, stressor, or social index scores, or for a single indicator of particular interest. This type of mapped product has the strength of being able to display screening results for the entire assessment area in a way that allows viewers to recognize individual areas they know, while also revealing geographic patterns such as clusters or corridors of good or bad scores. On the other hand, mapping is not well suited to displaying more than one or two factors for comparison at a time, and series of separate maps are usually needed to address multiple comparisons in a screening. Nevertheless, mapping is very effective at displaying screening results and stimulating discussions about possible geographically-based strategies to use recovery potential information in targeting restoration. See ways to use mapping (PDF) (4 pp, 653K, About PDF) in Recovery Potential Screening for more applications.

Previous: Step 4: Calculate summary scores | Next: Step 6: Refine your assessment


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