The pre-accident baseline is the expert’s best assessment of the claimant’s symptoms, function and future course immediately before the event. Without it, causation becomes little more than a comparison between the claimant’s present condition and an imagined state of perfect health.
Baseline is about function, not labels
A medical diagnosis tells only part of the story. Two claimants may both have a recorded history of lower back pain. One experienced a brief episode five years earlier and returned to unrestricted work. The other had continuing symptoms, regular medication and difficulty with heavier activities before the accident.
The diagnostic label is the same. The baseline is not, the expert should examine what the claimant could actually do before the event. Were they working full-time? Did they require help at home? Were they exercising, driving or caring for relatives? Were symptoms occasional and manageable, or had they already begun to restrict ordinary life?
This is particularly important in psychological claims. A claimant may have a history of anxiety without having an active anxiety disorder immediately before the accident. They may have taken antidepressant medication for several years while remaining stable and fully functional. Conversely, a claimant with no formal diagnosis may have been experiencing significant symptoms that were documented as sleep problems, work stress or unexplained physical complaints.
The baseline cannot be reduced to whether the records contain a particular diagnostic code.
The claimant’s account still matters
Medical records are an important source, but they were not written for litigation and do not provide a complete account of daily function. A patient may manage recurring symptoms without consulting their GP. They may use over-the-counter medication, adjust their activities or accept discomfort as normal. The absence of treatment does not always mean the absence of symptoms.
The expert should ask specific questions rather than accepting the broad statement that the claimant had no previous problems. When was the last episode? How long did it last? Was time taken away from work? Did the claimant recover fully? Were there activities they avoided before the index event? The answer should then be compared with the records, employment material and any other available evidence.
Where the sources differ, the report should preserve that difference. It may state that the claimant recalls full recovery while the records document continuing consultations. It should not quietly rewrite one account to match the other.
The GMC requires medical experts to provide accurate, objective and non-misleading evidence, identify the information supporting their conclusions and explain qualifications arising from conflicting evidence.
Establish the condition immediately before the event
A previous condition is not automatically part of the relevant baseline merely because it appears somewhere in the records.
An episode of depression fifteen years earlier may have little bearing on the claimant’s psychological state immediately before a road traffic accident. A history of recurrent depression with continuing medication and a recent relapse may be highly relevant. The expert should therefore consider recency, frequency, severity and recovery.
The same applies to physical symptoms. An old fracture that healed without restriction is different from progressive osteoarthritis that was already causing pain and would have worsened. A remote neck injury is different from an active course of treatment continuing on the date of the later collision.
The aim is not to compile every previous complaint. It is to identify the condition and level of function from which any accident-related change must be measured. A long medical history can make the report look thorough while obscuring the entries that matter.
Compare two possible courses
Once the baseline has been established, the expert must consider two histories. The first is what happened after the index event. The second is what would probably have happened had the event not occurred however, the second question is often neglected.
A claimant with established degenerative disease may have experienced some future deterioration in any event. A claimant with recurrent anxiety may have suffered another episode because of later work or family pressures. The fact that the accident caused an immediate worsening does not necessarily mean that every future symptom is attributable to it.
The expert should explain whether the event caused a new condition, aggravated an existing condition, accelerated an expected deterioration or produced a temporary increase in symptoms. Where possible, the report should estimate how long the accident-related difference is likely to persist. If a precise division cannot be made, the expert should say so and explain the limits of the available evidence.
Practice Direction 35 requires experts to consider all material facts, including those that may detract from their opinion, and to state when insufficient information prevents a definite conclusion.
Vulnerability does not defeat causation
A claimant is not denied compensation merely because an underlying vulnerability made the consequences more serious than they would have been for another person.
The broad legal principle is that a defendant takes the claimant as found. The Supreme Court has recently restated the familiar example that it is no answer to a negligently injured person that a stronger or less vulnerable individual would have suffered less harm.
That principle does not remove the need for a baseline.
The expert must still distinguish the harm caused by the event from symptoms, disability or care needs that would have existed without it. Guidance used in care claims similarly directs experts to identify requirements arising over and above those that would have been present in any event.
A claimant may therefore be unusually susceptible to psychological injury and still have a valid claim for the full condition triggered by the accident. A different claimant may already have been deteriorating and recover only the additional harm or acceleration caused by the event.
Vulnerability and pre-existing disability are not interchangeable.
Baseline affects more than diagnosis
A weak baseline analysis can distort almost every later opinion.
It can cause the expert to attribute longstanding medication to the accident, describe an existing work restriction as new or recommend care that was already being provided. It may also produce an unrealistic prognosis by comparing the claimant with perfect health rather than their probable uninjured course.
The baseline should inform: the nature of the accident-related injury, the degree of aggravation, the duration of additional symptoms, treatment needs, work capacity, care and assistance; and future prognosis. These opinions may involve several disciplines. An orthopaedic expert may require psychological evidence before deciding why disability has continued. A care expert may need clear medical guidance on which needs are new. Where the factual assumptions materially affect the opinion, they should be stated rather than hidden.
When the evidence is incomplete
Sometimes a reliable baseline cannot be established from the material supplied. Earlier GP records may be missing. Occupational health documents may be required. The claimant may give an uncertain history, or previous treatment may have taken place abroad.
The expert should identify what is missing and why it matters. They may provide alternative opinions based upon different factual assumptions or defer a concluded view until the relevant records are available. What they should not do is treat missing information as proof that no previous condition existed. The pre-accident baseline is not a search for reasons to reduce the claim. Nor is it an opportunity to disregard inconvenient history. It is the control against which the alleged change must be measured.
The expert who does not establish where the claimant started cannot reliably explain how far the accident moved them.
