Creating a Ranking System
There are several different ways that a community-wide ranking can be calculated, and which one you use depends on your goals for completing your assessment.
Some general approaches include:
1. Give “worst case scenario” – e.g., one high makes a high rating
2. Develop appropriate cut-offs – e.g.:
-3 or more highs = high
-0-1 highs = medium
-everybody else gets a low
3. Create relative ranking across a community
-rank by the largest to smallest number of highs and break into thirds so that 1/3 of community is high, 1/3 is medium, etc.
From our perspective, the first option gives the most accurate hazard rating because of the “weakest link” principle. This means that if, for example, a home has a vulnerable wood roof, it may not matter whether the siding is non-combustible because the roof material already poses such a severe hazard. However, some newer communities may not have any wood roofs due to zoning restrictions, and may choose instead, to go with a scheme as described in number two above.
Determining the best overall rating system to use depends on the goals of your assessment. For example, if unscreened vents are a particular problem in a neighborhood or community, it could be that any house with unscreened or improperly screened vents would receive a high rating.