Research demonstrates that the Mini-Mental State Examination (MMSE), a tool currently frequently used to detect and measure cognitive impairment, is actually not a great tool to detect/measure cognitive impairment when used once and by itself.

Arevalo-Rodriguez et al. (2015). Mini-Mental State Examination (MMSE) for the detection of Alzheimer's disease and other dementias in people with mild cognitive impairment (MCI). The Cochrane Database of Systematic Reviews. p. 25.

Arevalo-Rodriguez I.; Smailagic N.; Ciapponi A.; Sanchez-Perez E.; Giannakou A.; Figuls M.; Cullum S. (2015). "Mini-Mental Status Examination (MMSE) for the detection of Alzheimer's disease and other dementias in people with mild cognitive impairment (MCI)". Cochrane Database of Systematic Reviews (3): CD010783. doi:10.1002/14651858.CD010783.pub2. PMID 25740785.</ref>