Abstract: A method for maintaining a persistent master identifier includes receiving a first plurality of clusters including a first plurality of user device identifiers and at least one first cluster attribute associated with the first plurality of identifiers. The first plurality of user device identifiers is stored as separate entries in a master table. Each entry includes at least a persistent master identifier, a user device identifier contained within the identified cluster, and the at least one attribute associated with the identifier. A second plurality of clusters including a second plurality of user device identifiers and at least one attribute associated with the second plurality of identifiers is received. Persistence of each entry in the master table is determined based on a comparison between the second plurality of clusters and the master table. The second plurality of clusters is selectively associated with a persistent master identifier based on the comparison.