In order to ensure sufficient sample sizes, bioarchaelogical studies of individual health in prehistory must often rely on assemblages that demonstrate high inter-individual variability in skeletal completion. Determining whether higher insult frequencies in particular individuals result from their greater skeletal preservation is a key step in understanding ancient health and disease. This study uses a simple new z-score residual approach to control for inter-individual differences in skeletal completion while comparing multiple variables. To test this method, a sex- and age-balanced sample of 85 adult individuals was selected from five Middle and Late Woodland sites in Illinois: Helton (11GE540), Gibson (11C5), Ledders (11C132), Ray (11BR104,) and Carter (11GE624). Data on the frequency of nine different health indicators were collected, and statistically significant period- or sex-based differences in osteoarthritis, alveolar resorption, and hypoplasias were observed, illustrating the utility of this approach for bioarchaeologists concerned with the effects of skeletal completion on assessments of prehistoric health.