A computer system is provided that stores reference data records and event data records that each correspond to one of the reference data records. Tokens are generated from the reference data records and sorted into subsets. Each reference data record that has a given token is included in the corresponding subset. A correlation value is calculated between members (e.g., the reference data records) of the subsets. The correlation values are calculated by determining a common time, calculating a reference value, calculating a percentage difference from the reference value, and then determining a correlation value (e.g., a correlation coefficient) using the percentage difference.