Objective-To examine the total and domain-specific prevalence of verbally and physically abusive, socially inappropriate, and care-resistive behaviors according to the Minimum Data Set (MDS) compared with research instruments in nursing home residents with severe dementia.Design, Setting, and Methods-As part of a longitudinal observational study, MDS behavioral symptoms data were compared with corresponding items from the Ryden Aggression Scale and the Cohen-Mansfield Agitation Inventory for 15 nursing home residents with severe dementia. McNemar's test was used to compare the difference in the proportion of subjects who experienced any symptoms, as well as specific symptoms in several domains, according to the MDS and the research instruments. Additionally, temporal fluctuations in behavioral symptoms were descriptively and graphically summarized.Results-The MDS significantly underestimated both the total proportion of subjects experiencing any behavioral symptoms (P = .016), as well as the proportion of subjects experiencing verbally abusive symptoms (P < .002), physically abusive symptoms (P = .008), or socially inappropriate behaviors (P = .016) compared with corresponding items from the research instruments. Moreover, these behaviors exhibited considerable temporal instability, suggesting that the systematic daily collection of measures of behavioral disturbances is imperative during the week in which the MDS assessment is to be completed.Discussion-Albeit from a small study sample, our findings call into question the validity of the MDS behavioral symptom items as they are currently recorded, and suggest that a simple intervention of twice daily completion of a behavioral symptoms checklist containing the MDS items during the week of the assessment may significantly improve the accuracy of the recorded data. KeywordsNursing home aggression; MDS validity; behavioral outcome measurement Copyright © 2008 6 Assessments are required on admission, quarterly, annually, at discharge, and whenever there is a significant change in the resident's status. Since its implementation in nursing homes in 1991, the role of the MDS has expanded beyond scheduled assessments to identify care problems and tailor individualized care plans. It now also functions as a case-mix-based prospective reimbursement mechanism for Medicare and Medicaid, and as an indicator of the quality of care provided by LTC institutions. 7 Thus, the reliability and validity of the MDS as an assessment instrument are of paramount importance.Section E4 ("Behavioral Symptoms") of the MDS describes as its intent: "the assessment of the frequency, and alterability of behavioral symptoms in the last seven days that cause distress to the resident, or are distressing or disruptive to facility residents or staff members, even if staff and other residents appear to have adjusted to them." 6 The coding for the 5 specific items comprising Section E4 focuses on the resident's actions rather than his or her intent. Sources of information may include a rev...