The ERMI uses a log transformation. Why?
A. By using the logs of the concentrations, we can factor the significance of each mold into our evaluation. The sum of the logs of 1,000,000 and 1,000 (6 and 3, respectively) is 9. Using the sum of the logs tells us more about the mold burden, in this simple case represented by visible mold growth. In fact, both molds in this example contribute to the mold burden in significant ways, through visible growth and concentration of cells in the environment. The ERMI scale accounts for both the diversity, represented by the 36 species measured, and the concentration, as described by using the logs of each of the species.
