Introduction / Daniel N. Allen -- Statistical and Methodological Considerations When Using Cluster Analysis in Neuropsychological Research -- Application of Cluster Analysis to Investigate Neuropsychological Heterogeneity in Psychiatric and Neurological Patients / Gerald Goldstein -- Identifying Neurodevelopmental Stages of Memory from Childhood Through Adolescence with Cluster Analysis / Nicholas S. Thaler -- Classification of Traumatic Brain Injury Severity: A Neuropsychological Approach / Daniel N. Allen -- Concluding Remarks / Gerald Goldstein.