The Hilsenhoff Biotic Tolerance Index is a diagnostic metric used to identify samples with a high degree of pollution tolerant organisms. This index is on a scale from 0 to 10 with higher values indicating more tolerant organism, and more polluted conditions. The formula is ∑ (ni * ti ) / N, where ni is the number of individuals of the "i"th taxon, ti is the tolerance index value of that taxon, N is the total number of individuals in the sample assigned a Hilsenhoff Biotic Tolerance value; some taxa are not included.
If the organism you need is missing, first make sure the above is not checked. If you still cannot find it, contact Doug Henderson (Douglas.Henderson@KingCounty.gov) with its name, its parent taxon, e.g., a species's genus, and, if available, its TSN.