The author co-citation analysis (ACA) method is commonly used to group authors of reference papers. Since the traditional ACA method analyzes only first authors of reference papers, it disregards the contributions of other coauthors and can only group each first author into one cluster. This study proposes an innovative ACA algorithm called "complete author pair (CAP) algorithm", which groups complete author sets or reference papers into clusters and thus finds authors who may have expertise in more than one area. The CAP algorithm is implemented in two citation data banks that collected paper references from two ACM journals during 2002-2005. The results show that the CAP algorithm runs up to 90% of average precision in each citation bank when comparing against ACM CCS. (c) 2008 Elsevier Ltd. All rights reserved.