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Estimating a person's intelligence before illness struck matters because it gives doctors a baseline to compare against current test scores. The NARTNational Adult Reading Test, a test that estimates a person's earlier level of intelligence from how they read words.Read more → (National Adult Reading Test) asks a patient to read aloud a list of irregular words, such as 'yacht' or 'ache', whose pronunciation cannot be sounded out from normal spelling rules. Reading these words correctly relies on old, well-learned knowledge rather than active problem-solving. For example, imagine a retired teacher who now scores poorly on a memory test: knowing her estimated premorbid IQ (intelligence quotient, a standardised score of general cognitive ability) was high makes that low score far more meaningful. In practice, the NART gives that missing premorbid baseline, which a single memory test alone cannot supply.

The NARTNational Adult Reading Test, a test that estimates a person's earlier level of intelligence from how they read words.Read more → works because crystallised knowledge, vocabulary and word recognition built up over a lifetime, is relatively preserved in early dementia (a progressive decline in memory and thinking), even as fluid, on-the-spot reasoning declines. Reading irregular words draws on this stored knowledge rather than active problem-solving, so the score stays close to a person's true peak ability even as illness begins. Clinicians then compare the estimated premorbid IQ with a current test, such as the MMSE (Mini-Mental State ExaminationA brief, widely used bedside test that scores overall cognitive function.Read more →, a bedside cognitive test scored out of 30), to gauge how much someone has actually declined. Take a scientist whose NART-estimated IQ is very high but whose current MMSE score is only average: that gap suggests real cognitive decline rather than simply average ability. In practice, this comparison helps separate someone who was never highly able from someone who has genuinely lost function.

• Why can a reading test estimate ability from before an illness began?
• In which patient would a National Adult Reading Test estimate be least valid?
• Besides a reading test, which approach is used to estimate premorbid intellectual ability?

• NART (National Adult Reading Test), estimates premorbid IQ from preserved word-reading, unlike the MMSE, which measures current cognitive function.
• Crystallised knowledge, vocabulary and word recognition preserved in early dementia, whereas fluid reasoning declines early.
• Premorbid IQ, a person's estimated ability before illness, rather than their current test score.
• MMSE, measures present-day orientation, memory and language, unlike the NART's estimate of past peak ability.

• Processing speed is a don't-hold ability rather than what this test measures.
• A stable remitted mood disorder does not invalidate the estimate.
• The opposite is true, which is precisely why word reading is used as the estimate.
• Reading correlates well with verbal intelligence, which is why the estimate works.
• Reading is typically acquired in childhood, well before most acquired illnesses.

• Extract the defining phenomenology, duration, severity and functional-impact clues.
• Match the pattern to the most specific diagnostic or assessment construct.
• Actively test the closest look-alike against the missing or contradictory clue.
• Choose the precise term rather than a broader category that is merely compatible.