When it comes to the field of statistics, an ancillary statistic refers to any additional value that can be derived from a sample of data. Some of the most common synonyms for this term include auxiliary statistic, side information, and supplemental information. These synonyms all emphasize the idea that an ancillary statistic provides extra context or insight into a dataset beyond what is immediately evident in the raw numbers. Ancillary statistics are often used in conjunction with other analyses or as a way to better understand complex relationships or patterns within a dataset. Whether you refer to an ancillary statistic as a side information or supplemental data, the value that it can bring to statistical analysis cannot be overstated.