Fluorescent in situ hybridization has become an essential tool for diagnosing and monitoring hematological disease. Testing for minimal residual disease requires precise and accurate normal cut-offs. There is no consensus in the field on the correct method of establishing a normal reference range. We discuss and compare several proposed statistical methods to calculate normal reference ranges, including Gaussian statistics, the beta inverse function, and a binomial treatment of the data. We demonstrate that a binomial treatment of the data is an accurate and simple method to calculate a normal reference range.