Measurement challenges in dementia research result from the disjuncture between disease pathophysiology and clinical and research measures, due to imperfect validity and reliability. For example, performance on neuropsychological tests does not precisely reflect biological functioning and capacity of the brain. Similar measurement challenges pertain to measures of the consequences, severity, and progression of dementia, including functional dependency, neuropsychiatric symptoms and behavioral patterns.
Validity refers to whether a measurement instrument assesses the phenomenon of interest. Gold standard measures can be used to assess the validity of alternative measurements, but there is often no clear gold standard in dementia research. Measures valid for one group of people may not be valid for another, leading to biased estimates of disparities and risk factor effects.
Reliability is the proportion of variability in a measure explained by the construct of interest, as opposed to the proportion attributable to measurement error (random fluctuations in the measurement not reflecting changes in the underlying construct).