Objectives: No guidance currently exists as to the cognition threshold beyond which self-reported quality of life for older people with cognitive impairment and dementia is unreliable.

Methods: Older aged care residents (≥ 65 years) were randomly assigned to complete the EQ-5D-5L in computer-based (eye movements were tracked) or hard copy (participants were encouraged to 'think aloud') format. Cognition was assessed using the Mini-Mental State Examination (MMSE). Think aloud and eye tracking data were analysed by two raters, blinded to MMSE scores. At the participant level, predefined criteria were used to assign traffic light grades (green, amber, red). These grades indicate the extent to which extracted data elements provided evidence of self-report reliability. The MMSE-defined cognition threshold was determined following review of the distributions of assigned traffic light grades.

Results: Eighty-one residents participated and provided complete data (38 eye tracking, 43 think aloud). In the think aloud cohort, all participants with an MMSE score ≤ 23 (n = 10) received an amber or red grade, while 64% of participants with an MMSE score ≥ 24 (21 of 33) received green grades. In the eye tracking cohort, 68% of participants with an MMSE score ≥ 24 (15 of 22) received green grades. Of the 16 eye tracking participants with an MMSE score ≤ 23, 14 (88%) received an amber or red grade.

Conclusions: Most older residents with an MMSE score ≥ 24 have sufficient cognitive capacity to self-complete the EQ-5D-5L. More research is needed to better understand self-completion reliability for other quality-of-life instruments in cognitively impaired populations.