We used the MMSE score of the patients with AD as a measure of cognitive function partly because it is widely accepted in studies of dementia, and partly because other measures such as IADLs and Alzheimer's Disease Assessment Scale scores were available only for noninstitutionalized patients in our sample. Obviously, other indicators of patients' cognitive function can be and have been used as predictors of caregiving costs, although some of them should be used with caution. For example, ADL and IADL scores may easily capture the effects of impairments other than those directly attributable to AD. Thus, it would seem reasonable, or even mandatory, to introduce explanatory variables for patients' comorbid health conditions in any AD cost regressions when IADLs are used as measures of patients' cognitive function.
Ernst RL, Hay JW, Fenn C, Tinklenberg J, Yesavage JA. Clinical Predictors of the Indirect Costs of Alzheimer Disease—Reply. Arch Neurol. 1998;55(1):131. doi: