Tests were performed between phase scores obtained from right and left ribs; right rib IV phase scores and scores obtained from the others in the right rib series; and between right rib IV scores and a composite score composed of the average of an individual's phase scores (omitting rib IV). Left ribs IV-IX were found not to vary significantly from their right counterparts. Although only right rib II was found to vary significantly from rib IV, use of the other ribs in the series should be undertaken with caution due to questions about their statistical significance. Due to the apparent variability in the accuracy of estimations obtained from ribs other than the right fourth, a composite of rib series scores, if available, is preferable to single rib phase score analysis. These findings allow investigators a wider range of available techniques in the assessment of age of imperfectly preserved skeletal material. 11 tables and 25 references