Outlier ratios are ratios that differ greatly from most of the ratios in a sample. Depending on the magnitude and distribution of these atypical ratios, statistical measure may be distored and may not be representative of the population of properties being tested. The IAAO Standard on Ratio Studies achkowledges the issue of potential distortion, but also comments that "...triming is not mandatory...". The problem is deciding whether any trimming method produces a more representative sample. This article attempts to analyze various potential trimming methods to ascertain which, if any, tend to give better results.
Assessment sales ratio studies, Assessment ratios
Dornfest, A. S., Chizewsky, A., & Davis, P. (2004). Alternate methods of addressing ratio study outliers. Journal of Property Tax Assessment & Administration, 1(4), 5-14. Retrieved from https://researchexchange.iaao.org/jptaa/vol1/iss4/1