What Is Premorbid Functioning and How Is It Measured?

Premorbid functioning is how well a person thought, remembered and managed daily life before an illness or injury changed things. “Premorbid” simply means before the illness or injury. There is almost never a test from before, so clinicians have to reconstruct that earlier level from what they can measure afterward.¹ The reconstruction leans partly on abilities that tend to survive brain changes, which makes a test taken now a window on the past.²

Why Your Own Baseline Matters More Than an Average

Standard testing compares a person’s score with the average for people of the same age. Someone who was well above average and now scores average looks normal, even if they have lost ground.³ The opposite also happens: a person who always scored below average can look impaired when nothing has changed.

Take a former engineer and a person who left school early, both scoring 100 after a stroke. For the engineer, that may signal a substantial loss. For the other person, it may mean little or no change. The baseline estimate is what tells these two stories apart.

An estimate of earlier ability shows whether a decline happened and how large it is.⁴ It is used after head injuries and in conditions such as Alzheimer’s and Parkinson’s disease.⁵ In children with head injuries, actual scores fell below predicted earlier levels, and more severe injuries brought bigger gaps.⁶

Premorbid level is sometimes confused with cognitive reserve. Premorbid level is where your abilities stood before illness. Cognitive reserve is the brain’s capacity to cope with damage, built over a lifetime. Reports may mention both, but they answer different questions.

How Reading Tests Estimate Earlier Ability

The most common method asks the person to read aloud a list of words with irregular spellings. Pronouncing words like these depends on having learned them, not on working them out.⁷ Reading ability also tends to stay stable with age while other thinking skills decline.⁸ So reading scores work as a stand-in for earlier overall ability.

English spelling does not always show how a word sounds. A word like “debt” or “naïve” cannot be sounded out by rule, so the reader has to have met it before. Easy, regular words would not work, because almost any adult could read them whatever their earlier ability.

The person reads about 50 words aloud, one by one. The words grow rarer and more irregular down the list. There is no time pressure and no right way to guess, and it usually takes only a few minutes. The result is converted to an estimated IQ for comparison.

The National Adult Reading Test, or NART, has been the standard tool since 1982.⁹ It remains accepted as a valid estimate across a range of conditions.¹⁰ US reports more often list the Test of Premorbid Functioning (TOPF), the Wechsler Test of Adult Reading (WTAR), or the reading part of the WRAT-4.¹¹¹² In healthy adults, reading tests gave the most reliable estimates of full IQ.¹³ After brain injury, TOPF scores track overall IQ and verbal ability closely, but they track processing speed only weakly.¹⁴

Using Education, Work and School Records

Estimates can also draw on education level and work history.¹⁵ Formulas such as the Barona equation predict IQ from facts like age, education and occupation.¹⁶ Because a formula is built from large groups, it describes someone like you, not you, and two people with the same schooling and job can have very different real abilities. Schooling and occupation tend to track with ability, but they also reflect opportunity.

That shows in the results. The Barona formula underestimated people with IQs below 80 and overestimated those above 119,¹⁷ so formulas pull estimates toward the middle. Older formulas also need correcting for rising test scores over time, about 0.23 IQ points per year, and then perform well.¹⁸

Adding background facts to reading scores modestly improves accuracy.¹⁹ In one Australian clinical group, reading-only estimates overstated IQ, while combined estimates did not.²⁰ Some methods mix background with current tasks less affected by injury.²¹

Old school achievement or college entrance scores can be converted into an estimate of earlier IQ.²² Relatives may be asked to describe the person’s personality and habits before the injury.²³

If you are heading to an assessment, bring old report cards, standardized test scores or transcripts if you have them, plus a summary of jobs held and responsibilities. Details on languages spoken and any schooling outside the country help too, as does a relative who can describe earlier habits and abilities.

Self-reports are tricky after injury, because people with brain injury may misjudge how they used to be. Informants offer an outside view but have their own biases. Clinicians often weigh both.

When the Estimate Is Less Accurate

In mild dementia, word reading stays close to healthy levels. In moderate dementia, most verbal tasks are clearly impaired.²⁴ A reading-based estimate at that stage may set the baseline too low and hide decline. Even before diagnosis, people close to a neurodegenerative diagnosis already scored lower on vocabulary than healthy people.²⁵

In very early disease, reading scores can be trusted more because word knowledge has usually not slipped much, though it may already be slightly lowered. As dementia advances, even well-known words are lost, so the same test would suggest a lower earlier level than the person truly had.

Effort matters too. When people don’t give full effort, reading-based estimates fall noticeably, while background-only estimates are affected least.²⁶ A reading test needs the person to try, so someone who is tired, depressed, anxious or not trying may read fewer words correctly and appear to have been less able. Clinicians may include separate effort checks, tasks that are easy for nearly everyone who tries, so a poor result can raise a flag.

Estimators may be less valid for older adults from different cultural or language backgrounds.²⁷ Reading scores reflect quality of schooling, which differs across groups.²⁸ Tests also age: a Dutch reading test lost precision after decades as word familiarity shifted.²⁹

When you read an estimate in a report, treat the estimated IQ as a range, not one exact number. Check which method was used and whether background was included, and consider whether language or schooling affected the reading test. Asking the clinician how confident they are is reasonable.

Why Earlier Functioning Shapes Recovery

After traumatic brain injury, earlier status was linked to injury severity, daily skills, thinking and outcome.³⁰ Earlier status and thinking problems at six months mattered more for 12-month outcome than injury severity.³¹ So two people with similar injuries can recover very differently. Recovery depends on the person’s starting point as well as the injury, so doctors do not predict it from the brain scan or injury grade alone.

Families can put this to use by sharing an accurate history of earlier abilities with the rehab team and by setting goals relative to the person’s own former level. Progress will be judged against that baseline. Tracking changes over months is worthwhile, since six-month thinking skills predict later outcome. Predictions describe groups, not certainties, and rehabilitation can still improve skills.

Premorbid Adjustment in Schizophrenia and Psychosis

In psychosis evaluations, the term refers to social and school adjustment through childhood and adolescence, not test scores. Information comes from interviews and records.

Psychiatric reports often use the Premorbid Adjustment Scale (PAS).³² It rates childhood, early adolescence, late adolescence and adulthood. It covers friendships, sociability, schoolwork, fitting in at school and romantic relationships, from 0 normal to 6 severe.³³ Splitting the rating by life stage lets clinicians see whether functioning stayed steady, slowly slipped or dropped suddenly. Two people with the same overall score can have very different histories, such as one who always struggled and one who did well until their late teens.

Clinicians ask families how the person did with friends at different ages, how grades and behavior went over time, and when changes first appeared. They also ask whether withdrawal came gradually or suddenly.

About 3 in 10 people kept good adjustment until illness began.³⁴ Just over half started well and slowly declined before onset.³⁵ About 1 in 8 struggled from childhood and kept declining.³⁶ Falling school performance by late adolescence was common in both sexes,³⁷ because illness can show subtle signs before the first psychotic symptoms.³⁸

Poor childhood adjustment and decline in adolescence were linked to more withdrawal-type symptoms and poorer social functioning 20 years later.³⁹ Assessments give weight to earlier life stages to avoid mixing in early illness signs.⁴⁰

Brain Scans and Head Size as an Earlier Baseline

Research sometimes uses the space inside the skull, measured on MRI, as an estimate of brain size before illness.⁴¹ The skull does not shrink when the brain does, so it preserves a record of the earlier size. It is a widely used measure of brain reserve in research.⁴² Different measuring methods can give biased results, though.⁴³

On a patient’s scan, a report may compare brain volume to head size, which helps judge shrinkage relative to your own skull. It does not replace thinking tests for estimating earlier ability.

Estimates in Legal and Disability Cases

Estimating pre-injury ability is central in legal cases involving brain injury.⁴⁴ Courts expect methods that are scientifically sound and make obvious sense.⁴⁵

If you face a legal evaluation, gather school and employment records early and give full effort on every test. Expect evaluators on both sides to question the method, and ask how the estimate was chosen.