Method, Quantum, and the Limits of Joint Working Under CPR 35
Over the past year, my work as an expert witness has involved a significant number of expert meetings and Joint Statements across a range of quantum disputes. The reflections below draw on recurring themes from that work, with a focus on the method and behaviour of experts and on Joint Statement dynamics, which may be familiar to those involved in loss‑quantum disputes. The focus here is on losses from employment, but the same issues arise in cases involving business profits loss quantum.
Following exchange of reports, quantum experts are usually directed to hold an experts’ meeting, commonly conducted by telephone or video conference. That meeting is then followed by the drafting of a Joint Statement, intended to identify areas of agreement and disagreement in accordance with CPR 35.
In practice, the Joint Statement is rarely produced in a single pass. It is common for the document to go through multiple iterations as points are refined, clarified, or re‑expressed. In higher‑value personal injury and fatality claims, particularly where earnings, dependency, or long‑term loss assumptions are contested, the drafting process may involve ten or more versions before a final form is agreed and signed.
The process should not be adversarial, although in practice it can sometimes take on that character, and it is necessarily constrained. A Joint Statement is not a second report and is not designed to facilitate wholesale recalculation or re‑analysis; however, targeted recalculations do often take place where an opposing expert identifies a specific error, omission, or point requiring correction. Its primary function remains the accurate recording of the outcome of joint discussion.
It is within this setting that anchoring effects most commonly arise. Once a headline figure has been articulated early in the process, and then carried forward unchanged through successive drafts of a Joint Statement, the figure can acquire a degree of perceived solidity that is disproportionate to the extent to which its underlying assumptions have been tested.
Joint Statements Can Expose, Rather Than Resolve, Quantum Differences
In many cases, the difficulty is not a lack of expert evidence but an excess of apparently neat figures that do not withstand scrutiny.
Instructing solicitors will recognise situations where a Joint Statement process appears to have narrowed issues yet leaves an uncomfortable sense that something important has been smoothed over rather than resolved.
Method‑Led Analysis Versus Outcome Anchoring
A recurring distinction in quantum evidence is between analysis that is genuinely method‑led and analysis that appears anchored to an early numerical outcome.
A method‑led approach, with employment earnings losses, starts with an understanding of the important features of the role and sector in question. It distinguishes between different components of remuneration, recognises how earnings evolve with experience and responsibility over time, identifies uncertainty explicitly, and allows conclusions to emerge from tested assumptions. The process is similar in cases involving lost business profits or earnings.
By contrast, an outcome‑anchored approach tends to fix on a headline figure early and then defend it. Discussion shifts away from whether the inputs remain sound and towards whether the number can be preserved. Courts expect experts to test their numbers, not to protect them.
Fixed Figures and Anchoring Bias
In the case reflected on here, the opposing expert’s quantum figures remained unchanged despite acknowledged limitations in the underlying earnings data.
No recalculation was undertaken. No alternative scenarios were offered. No sensitivity analysis was produced.
Retaining a single unchanged figure in the face of recognised data limitations is itself an analytical choice.
Job Advert Data and Earnings Construction
The most substantive methodological disagreement concerned reliance on job advertisements sourced from online platforms with limited transparency as to data collection or verification.
By their nature, such sources typically exclude overtime, bonuses, allowances, and other variable remuneration. In sectors characterised by substantial overtime, seasonality, or performance‑related pay, basic salary alone may represent only part of total earnings.
What mattered was not the choice of source per se, but how its limitations were treated.
Once it was identified that the job‑advert data excluded variable remuneration, no attempt was made to assess the potential impact of that exclusion. The headline figures remained unchanged.
Experience is Flattened
A related limitation of job‑advert data is that it rarely captures the earnings impact of experience.
Advertised salaries are typically pitched at entry‑level or broadly defined roles and do not distinguish between newly appointed individuals and those with five, ten, or more years’ relevant experience.
Where experience materially affects responsibility, productivity, or seniority, reliance on undifferentiated advert figures risks flattening the earnings profile and understating likely pay progression.
An experience-banded approach, drawing on historical earnings data from reliable, transparent survey sources where available, supplemented with logical modelling, allows the court to assess quantum by reference to realistic career stages rather than a single static figure. Again, this is a methodological issue, not a difference of opinion.
Uncertainty is Not a Discount
Uncertainty should be identified, explained, and, where possible, modelled through alternative scenarios or ranges.
Uncertainty is not inherently downward‑biasing. Equally, uncertainty may justify caution in either direction; however, where data inputs are known to be incomplete, treating uncertainty solely as a reason to resist alternative outcomes risks converting it into a de facto discount mechanism.
Where acknowledged uncertainty is left unexplored, and only a single fixed outcome is presented, the absence of ranges, scenarios, or sensitivity analysis is not neutral; it is itself an analytical choice.
The Joint Statement: Clarification or Compression
A Joint Statement is intended to clarify areas of agreement and disagreement, not to act as a second report or a vehicle for advocacy.
In practice, pressure to narrow issues can result in disagreement being recorded narratively while headline figures remain unchanged. This can create the appearance of consensus without resolving the underlying analytical divergence.
Signing a Joint Statement does not signify endorsement of the opposing expert’s figures. It confirms only that the document accurately records the areas of agreement and disagreement reached through joint discussion.
It is also worth acknowledging a further dynamic that can arise once a Joint Statement has been completed. Where headline figures remain unchanged, the document may be received by the parties not as a prompt for further analytical testing, but as confirmation that positions have been successfully held.
Where this occurs, the Joint Statement can have the unintended effect of entrenching positions rather than encouraging further exploration of ranges, scenarios, or sensitivity, even where underlying factual differences have not been cross‑tested against the opposing case assumptions.
Seen in that light, the persistence of fixed figures following joint working is best understood not as a failure of the process, nor necessarily as a consequence of legitimately different factual cases, but as the product of analytical choices about whether, and how far, opposing assumptions are tested.
What Assists The Court
Where a material limitation is identified but no recalculation or sensitivity testing is undertaken, the court is left with a clear forensic question rather than a numerical answer.
That is not a failure of joint working. It is the proper outcome of disciplined expert engagement under CPR 35.
Concluding Observation
A quantum expert should not be judged by how firmly they defend a number, but by how rigorously they are prepared to test it.
Richard Formby FCA MAE
Get in touch to discuss your client’s case
