You want to establish whether a patient's reported misidentification of a family member is a brief, everyday experience or a persistent, elaborated pattern. Which single question is most useful?
Asking about duration and any change in actual behaviour toward the person directly tests the distinction the phenomenon's own text draws between brief, non-pathological experiences like déjà vu and persistent, elaborated misidentification requiring full assessment. Sleep, family history, and time of day are reasonable general background but don't test this specific distinction.
Key discriminating feature: The key distinction within this category is between a brief, self-limiting everyday experience and a persistent, elaborated, behaviour-changing misidentification, so asking about duration and behavioural impact together is the most efficient way to establish which is present.
References
- Casey, P. & Kelly, B. (2019). Fish's Clinical Psychopathology, 4th ed. Ch. 5, 'Disorders of Memory'.