Abstract: Presented herein are techniques for determining microsatellite instability. The techniques include generating a reference sample dataset representative of or mimicking a hypothetical matched sample for an individual sample of interest. The reference sample dataset may be generated from a set of reference normal samples that are not matched to the sample of interest. For samples of interest lacking a matched sample, the reference sample dataset may be used to determine microsatellite instability and to provide an indication of a presence, absence, or degree of microsatellite instability of the sample of interest. The reference sample dataset may be generated such that individual microsatelliate regions associated with a high degree of variability between ethnic groups are filtered out, masked, or otherwise not considered.