Subtle inefficiencies in everyday tasks indicate early functional difficulties in older adults: Implications for clinical practice and research

<b>Objectives</b>: This study investigated the validity and reliability of subtle errors and slowing in simple everyday tasks (Naturalistic Action Test [NAT]) to assess mild functional difficulties in older adults with mild cognitive impairmen (MCI). <b>Method</b>: Older adults (<i>N</i> = 111, MAge= 73.45; SD= 6.53) classified as having healthy cognition (HC) or MCI completed neuropsychological testing and two NAT tasks (breakfast and lunch) twice, separated by 4–6 wk. NATs were scored for subtle, inefficient actions (i.e., micro-errors) and the average time (in sec) to complete a task step. <b>Results:</b> Participants with MCI made significantly more micro-errors [<i>F</i> (1, 109) = 8.78, <i>p</i> = .004, partial <i>η</i>² = 0.07] and had a significantly longer average time per step [<i>F</i> (1, 109) = 13.98, <i>p</i> &lt; .001, partial <i>η²</i> = 0.11] than participants with HC. Micro-errors correlated with tests of episodic memory (<i>r</i> = −0.237, <i>p</i> = .012) and executive functioning (<i>r</i> = −0.201, <i>p</i> = .035), whereas average time per step correlated only with episodic memory (<i>r</i> = −0.300, <i>p</i> = .0001). Test-retest reliability was good for average time per step (ICC = .872, <i>p</i> &lt; .001) and moderate for micro-errors (ICC = .675, <i>p</i> &lt; .001). <b>Conclusions:</b> Measures of inefficient actions and performance time in familiar everyday tasks demonstrated strong to adequate construct and concurrent validity, as well as test-retest- and inter-rater reliability, supporting their use for the quantifying mild functional difficulties. Future studies should explore this scoring approach to develop early markers of functional disability or dementia risk.