Are the "Serial 7s" and Spelling Backwards Tasks From the MMSE Comparable in MCI and Dementia?

We explored the comparability of the "Serial 7s" (S7) and Spelling Backwards (SB) tasks from MMSE in 313 patients with MCI (N=54) and dementia (N=259) due to Alzheimer's disease (AD), frontotemporal lobar degeneration, Lewy body disease, non-AD degenerative (NADD), chronic cerebrovascular disease (CVD) or mixed (AD+CVD) etiologies. Although the two tasks were significantly associated with each other (r=.54), a two one-sided test revealed that they were not statistically equivalent. Consistently, a linear mixed model testing the effect of task Type (S7 vs. SB) net of demographics, disease duration, disease severity and etiology revealed that the S7 condition was more difficult to be performed (M=1.69) than the SB one (M=3.03). Hence, in MCI and dementia due to chronic-degenerative etiologies, the S7 and the SB tasks from the MMSE are not comparable. Users should exert caution when qualitatively interpreting examinees' attentional levels based on these tasks.