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Site Score

The scores of the four pathways (0 to 100) are combined by a root mean square method to give a single site score (0 to 100).

Scores are first calculated for the individual pathways and then are combined for the site using the following equation to determine the overall HRS site score:

HRS Rule , section 2.1.1, page 51587,

This method places an increased emphasis on higher scoring pathways. For example, a ten point increase in a pathways score from 50 to 60 points would raise the site score by 10 points. However, the inclusion of a new pathway with a score of 10 to a site already with a pathway scoring 50 points would result in an increase of about 1 point. Thus, information collected to improve a high pathway score has a potentially greater impact on the site score than does information collected to support the scoring of lower scoring pathways. Given an existing single-pathway score (A) less than 57, the additional score required for the same pathway to reach a site score of 28.50 is:

57 - A
whereas the score required for a second pathway is given by:

(3,249 - A2)½

For example, suppose a preliminary scoring effort resulted in a single-pathway score of 50. Within that same pathway, only (57 - 50) = 7 additional points would be required for a site score of 28.50, while in a different pathway, (3,249 - 2,500)½ = 27.3 points would be required. Knowing the two highest pathway scores usually is sufficient to determine whether the site score is likely to be above 28.50.

One important characteristic of this method is that the site score cannot be greater than the highest pathway score. Thus, the pathway likely to achieve the highest score should be evaluated first. If this pathway score is less than 28.50, no further evaluation is necessary: the site score will be less than 28.50. The table below is from the HRS Guidance Manual (Highlight 3-3) and shows further combinations of pathway scores.

Combination of Pathway Scores That Yield Site Score of 28.50

Individual Pathway Scores Sum of Squared Pathway Scores Site Score
57.00 0.00 0.00 0.00 3,249 28.50
40.31 40.31 0.00 0.00 3,250 28.50
32.91 32.91 32.91 0.00 3,249 28.50
28.50 28.50 28.50 28.50 3,249 28.50

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