Abstract: A robust Reference Interval estimator determines a Reference Interval from a data sample as small as 20 skewed data samples, even in the presence of outlier samples. This ability avoids expensive tests to increase the data sample or allows calculation of a Reference Interval when only a small cohort for sampling is available. First, a set of data samples are power transformed to remove a non-Gaussian skew to the set. Then, the Tukey approach is used to identify an outlier cutoff and the set of data samples are truncated to remove outlier data samples that are beyond the outlier cutoff. The truncated set of data samples are then used to compute the Reference Interval. The truncated sets of data samples are then also power transformed to compute the Reference Interval.