Robust opinions need robust reasoning: 15 medico-legal postulates

Expert opinion, one foundation of civil litigation and justice, should be based on robust reasoning. An unrelated namesake of the author, the microbiologist Robert Koch, formulated four criteria or postulates in 1884 designed to establish robust reasoning in a different field - microbiology. In Investigations into bacteria: The etiology of anthrax (1876), he cited key principles about the causative relationship between a microbe and a disease.

This concept of 'postulate' was also alluded to by the famous psychotherapist David Malan, in his seminal text 'Individual Psychotherapy and Science of Psychodynamics' (1979), referring to robust reasoning when theorising on valid explanations for psychological symptoms. Both these famous scientists, David Malan and Robert Koch, used the term 'postulate' to mean 'assume or assert truths as valid premises for discussion or reasoning' (Free Dictionary definition, 2015).

In the field of civil litigation, expert opinion can be operationalised in terms of a number of key postulates, called Koch's medico-legal postulates. These relate to the medico-legal contexts of pre- and post-index event history, multi-source evidence, diagnosis, causation, prognosis, and reliability. They have been arrived at following 20 years of experience in assessment and treatment of psychological injuries.

Koch's medico-legal postulates

I. A robust opinion should address diagnosis, causation and attribution, duration, and prognosis;

II. A robust opinion will, whenever possible, include more than one type of evidence. An opinion based on a claimant's self-report only may still be valid but is not considered as robust as an opinion derived from utilising several sources of data (e.g. self-report, medical records, impact upon other areas of functioning) in medico-legal terms;

III. The classification/diagnostic categories given in the Diagnostic and Statistical Manual of Mental Disorders (DSM) and the International Classification of Diseases (ICD) are a part of the formulation of an expert's opinion - this systematic check of relevant criteria should be balanced by wider clinical judgement and contemporaneous records, if available;

IV. The expert's mental state examination should be consistent with the claimant's description of currently active symptoms - a clear discrepancy reduces the robustness/strength of an opinion;

V. Wherever possible, the claimant's computerised GP attendance records should be made available to the expert. The subsequent analysis (i.e. evidence of or lack of corroborative data) will increase the strength or reliability of the opinion given;

VI. A therapist who has already treated a claimant cannot provide an impartial or independent expert opinion on issues of diagnosis, causation, or prognosis for that claimant;

VII. A robust opinion should include a history of factors which could, on the balance of probabilities, affect a specific index event reaction;

VIII. A robust opinion should give particular emphasis to the 12-month period before and after the index event, but not to the exclusion of earlier or later history;

IX. In any interview where the claimant displays a high level of affect, a differential opinion should be made between understandable presentation at interview when recalling a distressing or frustrating event involving perceived injustice and clinically significant adjustment problems which might require intervention;

X. An expert opinion should incrementally increase in robustness over time with access to more data and discussion with other relevant professionals, both legal and clinical;

XI. An expert's opinion should be the 'best fit' professional view of all available data at that time, and should be modified, if appropriate, as and when new data becomes available;

XII. When key evidence (e.g. medical records) is unavailable, the expert should state that the robustness of their opinion is reduced as a result;

XIII. It is incumbent on the expert to be impartial and independent of the instructing party, and to maintain as high a level of logicality as possible when appraising evidence;

XIV. Experts should maintain a high level of accessibility to lawyers in order to encourage and not hinder rapid process and resolution of litigation; and

XV. Experts should understand and be sympathetic to the claimant's experience of litigation stress, irrespective of their expert opinion on the specific case.

Whither these postulates?

Different experts will have their own varied set of beliefs underpinning their assessment methods. My postulates, in my opinion, account for 75 per cent of the variance in experts' opinions. However, as soon as this list is published, deficiencies will be recognised and discussed, no doubt. It is essential and informative to 'recognise the wider range of contemporary approaches to build an argument…and establish proof' (as stated by TJJ Inglis in 'Principia Aetiologica: Taking causability beyond Koch's postulates', 2007).

However, to date, these current postulates are based on congruence of a large number of assessments carried out by a team of more than 30 experts, exploring and understanding dissonance when it occurred, to assemble arguments for what constitutes robustness in opinion formulation.

Any process of suggesting postulates of universal applicability with any one field are, by nature, provisional and subject to further refinement in the light of future observation. In this particular field (personal injury and civil litigation), it is anticipated that this refinement will take place in areas of vulnerability to injury, prognosis/treatment, and mitigation of loss, as well as procedural areas such as joint opinion formation, deception detection, and reliability /truthfulness.

Dr Hugh Koch is a chartered clinical psychologist and director of Hugh Koch Associates. He is a fellow of the Expert Witness Institute and of the British Psychological Society