The relative moldiness index is the scaled scoring scale that turns a dust-DNA mold profile into a single number ranking a home against a national reference set of US houses. It is the index machinery underneath ERMI.
What is the relative moldiness index?
ERMI works by taking the log-transformed counts of 36 mold species from a dust sample, summing the water-damage (group 1) species and subtracting the common (group 2) species, and placing the result on a distribution built from a national EPA survey. A higher index means the home's dust profile skews toward water-damage molds relative to that national baseline (EPA, Mold research context). The index is the interpretive layer; the raw MSQPCR counts are the measurement. Because the reference set is national, an index value compares a home to "US homes generally," not to a local outdoor baseline the way an indoor-outdoor ratio does.
Why it matters to a mold inspection
The index is easy to present as a verdict, and that is the trap. It ranks accumulated dust against a national distribution; it does not confirm active growth, locate a source, or clear a remediation. The EPA developed the underlying method as a research tool and does not endorse it for routine assessment, a limit that has to travel with any index value an inspector reports (EPA, Mold and Health). Reported honestly, it is one historical data point. See ERMI explained and the ERMI vs air sampling comparison.
MoldMind stores an index value with its component species and the caveat that it is a research-derived ranking, so it is never presented as a standalone pass/fail.
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Sources
- EPA, Mold (research context): the moldiness index ranks a dust profile against a national reference distribution.
- EPA, Mold and Health: the underlying method is a research tool, not endorsed for routine assessment.