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Causation of Psychological Injuries and Index Incident Assessment

Special Reports

by Koch HCH & Newns K (2016).


Conducting psychological assessments for medicolegal purposes, in the area of psychological injuries following index events such as road traffic accidents, medical and work accidents, is a complex task as rarely does one event occur in total isolation from other events, trends or predispositions. Psychologists acting as experts are required to understand and debate theories of injury causation, conduct a qualitative (and sometimes quantitative) analysis of  data and attribution, and give a prognosis for future injuries with or without treatment. This discussion paper highlights the key issues inherent in these complex assessments.


The ability to reliably identify a psychological ‘injury’, to understand its causes and to establish appropriate attribution to a trigger event are crucial to the successful functioning of the civil court and to the law firms and the clinical experts who provide services to them. Ensuring and maximising evidential reliability
involves careful consideration of any pre-injury psychological issues, as well as any pre-event and post-event stressors (Leckart,2009). This process may well involve ‘apportionment’ i.e. the estimation of the percentage of psychological injury caused as a direct result of the index event, as opposed to other unrelated pre-event or post-event factors. The notion of apportionment is typically applied with respect to three time frames: prior to the index event, the index event period itself and, thirdly, at the time of the medico legal assessment period (typically 3 – 36 months later).

Effects of other adverse events

A common misconception is that the more ‘stressors’, or adverse life events, an individual has experienced  across the course of their lifetime, the more pathology and disability is apportioned to their previous history.

However, two important factors can run counter to this: a] the positive ‘toughening’ effect of adverse life experience resulting in resilience and increased coping ability for subsequent [e.g. index] stressors, and b] the time gap between previous life events and the index event, which may well have allowed the individual to resolve or otherwise overcome a previous trauma.

Of course a prior history of trauma can also leave the individual with a vulnerability or pre-disposition to later psychological problems. The balance between these issues in any one particular case requires careful consideration (Koch et al, 2014 a).

Furthermore, it is well known that symptoms of anxiety and depression are common in the general population. The UK-based NICE guidelines (2009) state that after one prior treated episode of depression, there is a 50% chance of a further episode within that individual’s lifetime. This raises the relevant medico-legal question – might the claimant not have had the particular symptoms claimed even if the litigated event had not occurred? This, essentially, is the powerful ‘but for’ question. their issues, which experts need to grapple with when assessing causation, include:

a) What were the effects of the claimant’s pre-event personality including their resilience, and tendency to minimise or maximise their distress?

b) Indication in their pre-event history of a significant predisposition of vulnerability to the development of further symptoms when experiencing stressful events?

c) To what extent do the frequency and severity of any pre-event episodes of psychological symptoms predict further such episodes at/or around the time of the index event?

d) Further, how might the above conflict with, or else confound, the ‘egg-shell skull’ principle, which insists that the Court must take the claimant ‘as it finds him/her’? (Koch, 2015)

Pre-event Stressors

There is no exhaustive list of possible stressors or adverse life events to investigate. However, the typology and list below illustrates some of the more typical events and issues to be considered:

a) Typology:

Work = Work accident (and injury), redundancy, fear of redundancy. Work harassment, conflict or disciplinary situation, significant work stress.

Traffic = Car accident, motorbike accident, cycle accident or pedestrian accident.

Medical = Significant medical illness, significant medical illness to partner, children or parents, termination, child birth.

Psychological = ongoing (chronic) or recent psychological symptoms (which may or may not be treated with psychological therapy or anti-depressants).

Social = Significant financial debts, marriage, divorce, separation and relationship difficulties (such as living apart).

Other = Childbirth, termination, house move, alcohol misuse, non-prescribed drug use. A checklist of stressful life events is shown in figure I below:-

Fig I
Work Accident and Injury
Fear of Redundancy
Work Harassment or Stress
Disciplinary Situation
Car Accident
Motorbike Accident
Cycle Accident
Pedestrian Accident
Significant Mental Illness
Hospital Stay
Medical Accident
House Move
Alcohol Misuse
Non-Prescribed Drug Use
Antidepressant Medication
Significant Financial Debts
Relationship problems or Separation
Neighbour Dispute
Bereavement or Serious Illness to Close
Relatives/Close Friend
Problems with your Childre

Theories of Injury Causation

Clinical and medico-legal experience has demonstrated that one of more events can result in a variety of independent or dependent (linked) outcomes. Two main theories that can apply are the Single Cause Theory (SCT) and The Domino Cause Theory (DCT) from Industrial research (RRC International, 2015).

SCT Theory predicts, in a simple, straight forward way, that a single index event occurs which causes a direct result, in terms of some form of psychological
symptom or injury, with no relevant antecedent events or context and no relevant post-index event events or context.

The DCT theory suggest that there is a sequence of one or more events or circumstances that affect or influence the emergence, severity and duration of psychological symptoms e.g. prior similar events (e.g. prior road accident), prior adverse events, vulnerability or predisposition/personality. The DCT also takes into account the legal concept of ‘Thin’ & ‘Crumbling’ skulls (Koch et al 2015). This multi-causal theory suggests that preceding an index event there is a combination of causal factors that lead to post index event psychological symptomatology. This model also presupposes that for most, if not all, individuals there is a threshold of coping, resilience and emotional wellbeing that needs to be ‘breeched’ or ‘overcome’ by one or more events in order that a clinically significant or diagnosable psychological injury to occur. Within this threshold, individuals may well experience ‘near misses’ or situations which ‘could have led to an accident’ but not develop a psychological injury.

A third multi-causality theory (MCT) which considers that there may be several independent causes that impact and result in a post-index event psychological
injury. This model is more complex than the SCT or DCT theories and involves a more advanced analysis.

When conducting an analysis of an index event, it is common to distinguish between an immediate cause(s) and underlying or antecedent causes. These underlying causes may be significant or ‘root’ causes, or contributory causes. It is not infrequent that a post-index event psychological injury occurs as a result of a multiple chain of events. Understanding this has diagnostic, attribution and prognostic implications.

Making a comparison with the world of physical accidents analysis (e.g. plane crashes), it is interesting to be aware of work by Reason (1990), an occupational
psychologist, who developed a model of accident causation for ‘organisational accidents’. He showed that organisational accidents do not typically arise from a single cause but from a combination of ‘acute’ and ‘latent’ failures. The acute failures are unsafe acts which have immediate effects on the integrity of the system. Latent failures are pre-existing, dormant circumstances and often unrecognised until they interact with an index event – they increase the likelihood of an active failure. Returning to our medico-legal context, the implication of this research is that we should be aware of and look for such ‘latent’ factors when conducting our own medicolegal assessments although it is difficult to assess relative attribution and subsequently quantum to these latent factors.

Recall Effects: Faulty Memory or Intent?

It is often observed that claimants appear to have difficulty in recalling full details of their own history. Initial questioning may result in gaps and inconsistences in recall, which on re-questioning and prompting can then be explored in more depth. These gaps can be due to the following memory effects and/or to motivational or intent effects. (Koch et al 2014) a).

Memory effects:

a) Short-term and long-term memory impairment.

b) Impaired concentration at interview.

Motivational effects:

a) The claimant’s lack of perceived relevance of particular areas of questioning.

b) The intention to mislead or perhaps overemphasize index event effects

Another important factor, which can amplify both memory and motivational effects, is the ‘recency effect’. In many interview situations, the index event is either the most recent event of any significance or, perhaps, one of two (or three) recent significant events. As a result of ongoing litigation, and the perceived emphasis of the assessment interview upon the index event, the event itself can acquire greater cognitive and emotional significance for the claimant. This can, understandably, result in other life events being placed rather further back in the claimant’s mind. This process, if not taken into consideration at interview, can adversely affect the quality of the claimant’s recall of their own previous history thereby affecting the validity of the information upon which the expert bases his/her opinion.

Level of symptomatology in 12-month pre-index event

One key medico-legal issue is to establish the extent to which any previous stressors resulted in any marked pre-existing anxiety or depressed mood (or other
psychological symptoms), which may have been ongoing at the time of the index event. From a medico-legal perspective, the individual must then be construed as someone with an ongoing or pre-existing problem at the time of the index event, rather than being a vulnerable person with a pre-disposition to develop anxiety, depressed mood or other psychological symptoms. In such circumstances, GP records and claimant self-report are used to assess the level of psychological distress during the immediate 6-12 month period prior to an index event.

Subsequently, a post-accident diagnosis such as “the claimant suffered an exacerbation of pre-existing symptoms” may be appropriate when it is clear that the claimant had pre-existing emotional difficulties at the time of the index event.

Attribution: Science or clinical clarity?

The process of apportionment can be a subjective judgment, whereby the expert simply ‘pulls a number out of the hat’ citing the use of ‘clinical judgment’ from years of professional experience. Obviously, this is neither acceptable nor scientific.

When more than one adverse event exists, some form of quantitative apportionment is requested and required.

The three models that have been promulgated to assess relative attribution are:

1. GAF score comparisons,

2. Mixed mathematic/linguistic valuation (MMLV) and

3. Non-mathematical impressions (NMI).

1) GAF (Global Assessment of Functioning) scores: Leckart (2009) stated that the overall clinical assessment requested by the GAF score allows a numerical
comparison of assessments at different occasions in the claimant’s history.

This approach involves identifying the particular ‘baseline’ GAF score that best describes the claimant prior to the injury in question (and just after the index event), which is then compared to a GAF score representing the claimant’s level of functioning at the time of assessment.

The baseline GAF score is readily determined through a careful clinical interview and inspection of the medical records. In terms of ‘functioning’ this process helps establish what the individual could and could not do and their level of feeling, thinking and behaving before the most recent injury.

Then, the claimant’s immediate post-event and current GAF scores are determined in the same way. With simple arithmetic, the net result is an apportionment
figure. It is recorded as a simple number on a 100-point scale or as a range (e.g. 65 – 70). Its greatest utility is in assessing changes in a claimant’s level of functioning across time.

2) Mixed mathematic/linguistic valuation (or MMLV) allows the use of broad, common-sense categories to be used to represent attribution in terms of labels such
as: predominantly (over 50%); partly (49% or less), materially (33% or more with clarification).

This valuation can be aided by the use of a “Likert scale” where the Claimant is asked to describe their pre-accident difficulties on a scale of 0-10 and then rate these again post-accident.

3) Non-mathematical impressions (or NMI) is a procedure in which the examiner elects not state attribution in any substantive or concrete way, preferring the use of descriptive terms only such as ‘predominantly’, ‘partially’.

Whichever approach is taken, it is always important to have established a comprehensive history in which the individual’s adverse experiences are catalogued and their reactions and styles of dealing with those events are determined. At that point the psychologist’s job is to assess how the individual’s personality and previous experiences affect how they view the current, litigated stressor to form a subjective opinion about what proportion of the current psychological disability is due to the litigated event and what proportion is due to other factors.

Many cases involve situations in which the ‘psychological’ claim is as a result of a ‘physical’ injury, which in turn, has been apportioned from an orthopaedic
perspective. Naturally, a psychologist does not simply transpose the orthopaedic apportionment percentage since this, typically, does not take into consideration the psychological symptoms, e.g. the emotional impact of chronic pain and the psychological impact of not being able to function physically, as before, in one’s everyday life.

Further ‘apportionment’ complications arise in situations where there are multiple index events/accidents to consider; for example, if two or three traffic accidents have occurred within a short period of time. In these circumstances, symptoms can appear to ‘overlap’. It is then incumbent upon the expert to decide, clinically, how much of the current morbidity/injury is attributable to each of the accidents. This process involves identifying proportionality such as ‘33% x 3’ or ‘50% x1’ and ‘25% x 2’. It is also likely that no rigorous or scientific procedure can be applied in such circumstances and the examiner will have to resort to their subjective judgment.

Sources of data

In exploring history and the aetiology of the alleged psychological ‘injury’, the five main sources of data are the claimant’s subjective self-report, the results of the doctor’s Mental State Examination, the objective psychological testing results (if available), any contemporaneous records (GP, hospital; occupational health) plus any other collateral sources of information such as witness statement from relatives, friends and colleagues. Generally, when an expert has difficulties in identifying causation, the problem lies in having insufficient or inadequate data from these sources (Leckart, 2010; Koch et al 2014 b).

The validation of a claimant’s self-report is partly achieved by a review of medical or occupational records. It is also dependent on the claimant’s clinical presentation, which might include vagueness, evasiveness, and/or an over-dramatized or unrealistic presentation. The issues inherent with this review have been considered elsewhere (Koch, Lillie and Kevan, 2006).

With specific reference to attribution and causation, the following GP-record related information is pertinent:

1. Mention of index or other accidents.

2. Mention of relevant adverse events (pre- or post-index event).

3. Mention of psychological symptoms and, where present, their severity and duration as well as the treatment provided (e.g. psychotropic medication or referral to a specialist service) linked to the index event.

4. Medical certification for psychological symptoms.


Causation is central to every legal case (Young, 2015). The index event may be ‘material’ or ‘contributory’ to an injury, and must be seen in the multifactorial array of the available evidence. The expert needs to analyse
this from a biopsychosocial perspective taking into account pre-existing, precipitating and perpetuating factors, plus also taking into consideration personal and social resilience and protective factors. He must also apply logicality and, where possible mathematic apportionment to the expression of a robust opinion which cogently reflects a theory of causation which is as scientific and reliable as possible.

At a legal level, according to Young (2015), the ‘but-for’ test of causality stance constitutes a high bar for criminal cases and less stringent in the Tort context. An index event in a personal injury case can contribute materially and substantially to a resultant liable psychological injury although not uniquely or even majorly so (Young, 2015).

It is our view that the medical/clinical and legal fields need to consider Young’s concept of ‘biopsychosocial’ causality in order to specific its multifactorial components and interaction (Young, 2015). Judicial and medico-legal decision making in relation to multifactorial attribution needs further debate. 


Koch HCH, Leckart B, Shannon K & Hetherton J (2014 (b)) Reviewing Medical Notes. Expert Witness Journal. Autumn.

Koch HCH, Leckart B, Willows J & Lucas V (2014 (a)) What resulted from the index event? The dilemmas of causation and apportioning psychological distress. Expert Witness Journal. Summer.

Koch HCH, Lillie F.J. & Kevan T. (2006) Perfect Attendance: Decision Making Model for assessing the significance of GP attendance records – Legal – Medical 16-17 January

Koch HCH, Vallano J, De Haro L (2015) Thin or Crumbling skulls: Recommendations for applying these rules consistently to pre-existing status. Solicitors Journal.

Leckart B (2010) Apportioning Psychiatric Injuries. www.drleckhartwetc.com. December 1.23.

NICE (2009) Depression in Adults: Recognition and Management. CG90. www.nice.org.uk.

Reason J (1990) Human Error. Cambridge University Press, UK.

RRC International (2015) Loss Causation and Incident Investigation. RRC. London.

Young G (2015) Causality in Criminal Forensic and in Civil Disability Cases: Legal and Psychological Comparison. Int J Law Psychiatry. 42-43, 114-120.

Dr Hugh Koch and Dr Katie Newns can be contacted at www.hughkochassociates.co.uk.

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