Epidemiology and Litigation--The Sellafield Childhood Leukaemia Cases

Epidemiology and Litigation--The Sellafield Childhood Leukaemia CasesAuthor(s): Richard WakefordSource: Journal of the Royal Statistical Society. Series A (Statistics in Society), Vol. 161, No. 3(1998), pp. 313-325Published by: Wiley for the Royal Statistical SocietyStable URL: http://www.jstor.org/stable/2983205 .

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J. R. Statist. Soc. A (1998) 161, Part 3, pp. 313-325

Epidemiology and litigation-the Sellafield childhood leukaemia cases

Richard Wakefordt British Nuclear Fuels plc, Warrington, UK

[Received October 1996. Revised October 1997]

Summary. Statisticians and scientists are often required to provide information outside the scientific community. One important example is as an expert witness in the law courts. The civil litigation cases of Reay versus British Nuclear Fuels plc and Hope versus British Nuclear Fuels plc are a vivid illustration of how science and scientists interact with the law and lawyers. The personal injury cases were decided on the basis of how a specific epidemiological association should be properly inter- preted, and this involved many experts. It is desirable that statisticians and scientists understand the nature of expert evidence, and these two cases are used to illuminate the role of the scientist in civil litigation.

Keywords: Association and causation; Expert evidence; Ionizing radiation; Legal judgments; Legal process; Science and law

1. Introduction

Between October 26th, 1992, and June 29th, 1993, the civil law cases of Reay versus British Nuclear Fuels (BNF) plc and Hope versus BNF plc were heard concurrently in the High Court of Justice, London. These two personal injury actions were among the longest, most expensive and most complex to come before the English courts. The claims were that infant leukaemia (Reay) and non-Hodgkin lymphoma (NHL) affecting a young woman (Hope) had been caused by direct exposure to ionizing radiation or by exposure of one or both parents. The source of this exposure was the nuclear complex at Sellafield (formerly Windscale and Calder Works) in West Cumbria, England, run by BNF or, before 1971, the United Kingdom Atomic Energy Authority (UKAEA). The great majority of the 90 days for which the court sat was spent hearing expert scientific evidence, and judgment was based on this evidence rather than points of law. A significant fraction of the scientific evidence concerned epidemiology and the interpretation of epidemiological findings.

It is not my intention to review in detail the scientific evidence put before the court. This has already been done by several authors (Doll et al., 1994; Neel, 1994; Wakeford and Tawn, 1994; Tawn, 1995; Gray et al., 1995; Kite and Anderson, 1996; Tawn and Wakeford, 1997). In addition, Inskip (1996) has described her experiences as a scientist unintentionally caught up in the legal process, and Evans (1996) has briefly commented on issues raised by these cases from the point of view of an expert who appeared in court on behalf of the plaintiffs (Reay and Hope). The judgment has been published in full and commented on in the legal literature (French, 1994; Bowden and Isted, 1994) and also commented on by lawyers in the scientific literature (Bowden, 1995, 1996; Bowden and Isted, 1996). As a scientist employed

tAddress for correspondence: British Nuclear Fuels plc, Risley, Warrington, WA3 6AS, UK. E-mail: [email protected]

? 1998 Royal Statistical Society 0964-1998/98/161313



314 R. Wakeford

by the defendants (BNF) to assess radiological risks, I have been deeply involved with the technical issues underlying these cases for more than a decade. Consequently, I became directly and intimately concerned in the defence of these claims from the start of the legal process in the late 1980s until judgment was delivered in October 1993. I co-ordinated the defendants' technical evidence across a range of disciplines and was responsible for the technical structure of the epidemiological defence case. I took part in many long and exhausting meetings with lawyers and sat through the great majority of the presentation of the expert evidence in court, as well as appearing as an expert witness myself. My intention is to use my experience of the legal process in these two cases to illustrate the way that scientists, and in particular epidemiologists and statisticians, interact with the legal system, either in- tentionally or unintentionally, and why it is of importance for scientists to understand the nature of this interaction.

2. Background to the legal cases

In 1984, the Independent Advisory Group (chaired by Sir Douglas Black) confirmed a media report of an approximately tenfold excess of leukaemia among young people living in the coastal village of Seascale about 3 km south of Sellafield (Black Advisory Group, 1984). This excess was based on seven cases diagnosed in people while under 25 years of age in the period since 1950, when nuclear operations began at Sellafield. The Black Advisory Group could not identify the cause of this excess, including radiation exposure due to Sellafield, and made several recommendations for research to be carried out to clarify areas of uncertainty. One of the recommendations of the Group was that a body 'with significant health representation' should be set up to examine the effect of radioactive discharges into the environment, and, as a consequence, the Committee on Medical Aspects of Radiation in the Environment was established in 1985. The first task of the Committee was to re-examine the risk of radiation- induced childhood leukaemia in Seascale following suggestions that certain discharges of radioactive material from Sellafield, particularly during the 1950s, had been underestimated, and this was the subject of the first report of the Committee on Medical Aspects of Radiation in the Environment (1986). This report confirmed the need to revise data for certain releases and noted that this was unsatisfactory, but concluded that 'the substance and essential conclusions of the Black Advisory Group Report remain unchanged'.

The Black Advisory Group (1984) further recommended that cohort studies be conducted for children born in Seascale and for children attending schools in Seascale but born outside the village. The results of these studies were published in 1987 (Gardner et al., 1987a, b) and confirmed the excess of childhood leukaemia identified by the earlier geographical correlation studies, although the excess appeared to be concentrated among those born in Seascale. This raised the question of whether one or more causal factors might be 'acting on a locality specific basis before birth or early in life' (Gardner et al., 1987a).

In 1986, a report was published of an approximately tenfold excess of leukaemia among young people who were less than 25 years of age resident within 121 km of the Dounreay nuclear establishment in northern Scotland (Heasman et al., 1986). This excess was based on five cases during the period 1979-1984. Sellafield and Dounreay are the only two sites in Britain to carry out large scale spent nuclear fuel reprocessing operations. The Committee on Medical Aspects of Radiation in the Environment investigated this report and confirmed the excess of childhood leukaemia in the area around Dounreay, although noting that the magnitude and statistical significance of this excess depended strongly on the space and time boundaries selected. Again, the cause of the excess could not be identified, but the Committee



Epidemiology and Litigation 315

on Medical Aspects of Radiation in the Environment (1988) concluded that 'some feature' of the two sites was leading to an increased risk of childhood leukaemia in their vicinity.

It was after the publication of the Committee's second report in June 1988 that legal action on behalf of those who had developed leukaemia (or the related malignant disease NHL) while living near Sellafield, or on behalf of their families, came to be seriously considered. In July 1988, the London firm of solicitors, Leighs (later Leigh Day & Co.) placed an adver- tisement in The Whitehaven News, the local newspaper serving the area around Sellafield, inviting those interested in making a claim to contact the firm. As a consequence, writs claiming damages for personal injury were issued (but not served) in 1989.

By 1989, epidemiological evidence was available suggesting levels of childhood leukaemia that were higher than expected near several nuclear facilities in Britain (Gardner, 1989; Wakeford et al., 1989). However, the interpretation of these findings was not clear (Gardner, 1989; Wakeford et al., 1989, 1991; Wakeford, 1990; MacMahon, 1992). Scientific work which had been carried out since the report of the Black Advisory Group had demonstrated that

'it is most unlikely that sufficiently large errors exist in the estimates of directly delivered dose or of resultant leukaemia risk'

for radioactive discharges to account for the excess cases (Wheldon, 1989), the conclusion also reached by Stather et al. (1988). However, in 1990, the findings of the West Cumbria leukaemia and lymphoma case-control study suggested that an indirect mechanism of radiation exposure might be responsible for the childhood leukaemia excesses.

The West Cumbria case-control study was carried out by Martin Gardner and his colleagues on the recommendation of the Black Advisory Group (1984), and in February 1990 the initial results of this study of cases of leukaemia and lymphoma among young people born in West Cumbria and diagnosed there during 1950-1985 were published (Gardner et al., 1990). Each case was matched with two (possibly overlapping) sets of up to eight children without cancer. Many factors of possible relevance to the childhood leukaemia excess in Seascale were examined in this study, but the most striking finding was a statistically significant association between relatively high radiation doses measured by film badges worn by men while employed at Sellafield before the conception of their children and the incidence of leukaemia (and of leukaemia combined with NHL) in these children. Two preconceptional doses were considered: the cumulative dose and that received in the 6 months before conception. Point estimates of relative risk of 4.3-8.4 were obtained for the highest dose groups (100 mSv and greater and 10 mSv and greater for the cumulative and 6-months' doses respectively), but as these estimates were based on (the same) four cases of leukaemia and a similarly small number of controls lower 95% confidence limits were in the range 1.1-1.7. Gardner et al. (1990) suggested that the association could explain statistically the excess of childhood leukaemia in Seascale, and so the study had apparently achieved its objective.

The findings of the West Cumbria study received very substantial media coverage, and within a few weeks of publication writs were served on BNF claiming that either leukaemia or NHL had been caused by radiation exposure due to operations at Sellafield. The claims were amended to include specifically the exposure to radiation of the parents before conception of the children, in particular the occupational exposure of the fathers. One claim, on behalf of a child who subsequently died of leukaemia in September 1990, was not pursued in the first tranche of claims that were brought before the court. The trial was concerned with the concurrent hearing of the Reay and Hope cases, which were effectively pursued as 'test-cases'.

Dorothy Reay was born in 1961 in the town of Whitehaven, about 13 km north of Sellafield, and she died there at the age of 10 months of acute leukaemia. Vivien Hope was



316 R. Wakeford

born in 1965 in Drigg, a village about 6 km south of Sellafield. At the age of 6 years, she moved with her family to Seascale and in 1988, at the age of 23 years and while still resident in the village, she was diagnosed as having NHL. Both of the fathers were employed at Sellafield before the conception of the children. Reay was included in the study of Gardner et al. (1990), but Hope was not, NHL having been diagnosed after 1985.

3. Initial considerations in the legal cases

The first question facing BNF when served with the writs was whether to defend the claims or to settle them out of court. Whereas settling the claims would have cost a few hundred thousand pounds at most, it had to be expected that the defence of the claims would cost several million pounds. Superficially, settling would have been the most cost-effective option. However, there were weighty issues to be considered in the Reay and Hope cases that were beyond simple financial accountancy, including the adequacy of the scientific basis of radiological protection.

It must be appreciated that the plaintiffs were asking the court to find that, on the balance of probabilities, exposure to ionizing radiation resulting from operations at Sellafield was the cause or a material contributory cause of the malignant diseases in the particular individuals who were the subject of the claims. They had to place evidence to this effect, and to argue their case, before a single judge with no technical assessor or jury. In other words, they had to persuade a High Court judge that it was more likely than not that radiation exposure due to operations at Sellafield played a significant role in the development of these specific malig- nancies. Under the relevant legislation covering injuries caused by exposure to radiation resulting from the operation of nuclear installations, the judge was concerned solely with causation and the question of negligence on the part of the defendants (which would have to be established by the plaintiffs if, for example, exposure to chemicals had been the alleged cause) did not arise. Since it was evident that occupational exposure to radiation of the fathers while employed at Sellafield was likely to be the main plank of the plaintiffs' case, it was apparent from the beginning that the statistical association between paternal preconceptional radiation dose and childhood leukaemia found in the study of Gardner et al. (1990) would be central in any trial. There was little question that both Mr Reay and Mr Hope had received cumulative preconceptional doses in excess of 100 mSv (although only Mr Reay had received a dose exceeding 10 mSv in the 6 months immediately preceding conception), and therefore the scientific interpretation of the association would be the principal issue.

The plaintiffs had decided to bring these cases before the court on the basis of the evidence which was available to them at the time, and it was for them to convince the judge that, on the balance of probabilities, their claims were valid on the strength of this evidence. The defendants did not have to show an alternative cause, only that the plaintiffs had not made out their case. The judge, therefore, had to deal with considerably more than the possibility that exposure of parents to radiation could give rise to childhood leukaemia or NHL; he had to assess the veracity of specific claims concerning specific injuries to specific individuals on the basis of the evidence put before him. The judge had to be satisfied that the available evidence either was or was not sufficient for the defendants to be held liable for these particular personal injuries.

It was in this context that the defendants reviewed the scientific literature to determine to what degree a direct causal interpretation of the epidemiological association found by Gardner et al. (1990) could be supported. In their third report the Committee on Medical Aspects of




Radiation in the Environment (1989) had considered possible mechanisms whereby the occupational exposure of adults could be relevant to the induction of childhood cancer, including preconceptional irradiation, and had concluded that such mechanisms were 'highly speculative'. Gardner et al. (1990) had noted that the association was 'the first of its kind with human data' and this was reiterated by Beral (1990) in an accompanying editorial. (A report of a workshop held at the National Radiological Protection Board, Chilton, on May 9th, 1990, provides an interesting insight into the scientific discussions that were taking place in the immediate aftermath of the publication of the results of the West Cumbria study (National Radiological Protection Board, 1991).) BNF concluded that, on the basis of the available scientific evidence, the cases should be defended. This position was reinforced by an interim 'Statement of advice to Government' by the Committee on Medical Aspects of Radiation in the Environment (1990), published on April 2nd, 1990, which noted that

'The important conclusions of this study are unavoidably based on very small numbers, and as these are novel observations which have not been recorded previously, we are cautious in our interpretation. Further evidence from other studies currently underway and planned will enable us to make a firmer assessment of the implications of these results.'

Martin Gardner was a member of the Committee when this statement was issued. In defending the claims, BNF was not denying that direct exposure to radiation increases

the risk of cancer in the exposed individual or the risk of hereditary effects in the individual's descendants. Indeed, in the early 1980s, BNF with its trades unions pioneered the establishment of a scheme to compensate employees who had developed cancers which could have been caused by occupational exposure to radiation (Wakeford et al., 1998). What was contested was that the doses received by direct exposure of the two individuals to radioactivity from Sellafield were anywhere near sufficiently high to be a likely cause of the malignant diseases under consideration, or that it had been established that paternal irradiation at occupational (or, indeed, any) levels materially increases the risk of childhood leukaemia (or NHL) in offspring, in contrast with recognized radiation-induced hereditary effects such as congenital malformations.

It was clear from the outset that the plaintiffs would have to demonstrate one of two possibilities (or some combination of the two). The first possibility was that the risk of childhood leukaemia and NHL arising from direct exposure had been appreciably underestimated. This was a formidable task since this possibility had been examined in considerable detail from 1983 onwards and would require the identification of gross errors in the radiological assessments which had previously gone unrecognized. The second possibility was that exposure to radiation of the fathers while employed at Sellafield had led to the development of the malignant diseases. The evidence and hence the trial came to be very much concentrated on this second possibility, to the extent that the plaintiffs did not put before the court any substantial evidence on doses arising from radioactive discharges but confined themselves largely to cross-examining the defendants' experts on their evidence. (This was so, even though writs claiming damages had initially been issued before the publication of Gardner et al. (1990).) To demonstrate that paternal preconceptional irradiation was the cause or a material contributory cause in these two specific cases, the plaintiffs were almost wholly dependent on a causal explanation of the initial results of the West Cumbria case- control study. Conversely, they had to show that evidence against a cause-and-effect explanation was either flawed, or irrelevant or inconsequential. Thus, the plaintiffs' case inevitably came to be founded on the validity of the association between paternal dose and childhood leukaemia reported by Gardner et al. (1990) and a direct causal interpretation of



318 R. Wakeford

this association or, at least, an interpretation substantially involving radiation exposure due to operations at Sellafield.

4. Preparing for the trial

Once the two legal actions were under way, each side was obliged to make available to the other side any document that they had (or controlled) which was of relevance to the issues involved in the litigation, in a legal process called 'discovery'. As far as BNF and the UKAEA were concerned, this was an enormous task since it covered events over a period of almost 40 years. Offices and archives had to be meticulously searched for any document which could be pertinent, no matter what security classification, including personal notes, internal memoranda, internal reports, committee minutes and log-books. Tens of thousands of documents were reviewed for relevance in this process, and several thousand were copied and made available confidentially to the plaintiffs. The plaintiffs, in turn, had to review these documents for preparing expert evidence. This whole process took approximately 2 years.

One particular matter that came to play an important role in the preparation of expert evidence was the accuracy and completeness of the radiation dose records for Mr Reay and Mr Hope, and for the fathers in the West Cumbria case-control study. It was known that Gardner et al. (1990) had calculated preconceptional doses from a database of annual summaries of the readings of film badges that were routinely issued to radiation workers, maintained at Sellafield for epidemiological research. Quite apart from the question of the accuracy of the process of generating annual dose summaries from original film badge records, and the combining of these annual doses appropriately to generate preconceptional doses (illustrated by the need for Gardner (1992) to modify slightly the initial results of the West Cumbria study), was the matter of additional doses. Thus, it was recognized by Gardner et al. (1990) that doses to the testes from internally deposited radionuclides were not included in the preconceptional doses used in the West Cumbria study. It was also known that monitoring for exposure to neutrons in the earlier years of operations at Sellafield did not occur at an individual level but at a workplace level, and that neutron doses had not been entered into individual dose records under these circumstances. Further, the accuracy of early film badges in terms of recording photon doses under various conditions of exposure was uncertain. (These occupational dosimetry points have been discussed by Kite and Anderson (1996).)

These dosimetry matters were pursued with vigour by the plaintiffs, but these issues also placed the plaintiffs in a quandary in the preparation of their case. Since the effect of the occupational dosimetry uncertainties could vary quite considerably between employees and over time, it was not obvious what the effect of the changes to individual doses would be on the results of the West Cumbria case-control study, casting doubt on the robustness of the association which had become the mainstay of the plaintiffs' case. As a consequence, the plaintiffs concluded that they needed to obtain the results of a reanalysis of the West Cumbria case-control data using revised occupational doses.

This need was reinforced by the requirement on the plaintiffs to demonstrate the validity of the occupational dose associations to the court. The claimed causal link between paternal irradiation and childhood leukaemia was of such importance to the plaintiffs' case and this link was so heavily dependent on the results of the West Cumbria case-control study that the defendants could not afford to accept that no error had been made in such a complex study. The defendants, then, required the plaintiffs to prove in evidence that the associations concerning paternal radiation exposure at Sellafield were real. This could have been done by




having Martin Gardner or one of his co-workers give evidence to this effect in court. However, neither Gardner nor his colleagues were willing to appear on behalf of either party in the litigation. As Inskip (1996) has noted, this avoidance of partisan involvement is understandable, since it could have adversely affected the willingness of certain subjects to become involved in follow-up studies. The plaintiffs, therefore, were basically left with two options if they wanted to pursue this aspect of their claim: the rather unsatisfactory arrange- ment of forcing Martin Gardner or his colleagues to give evidence in court, or to repeat, independently of Gardner and his co-workers, the analyses conducted in the West Cumbria study with the various identified uncertainties addressed. It was the second option which was pursued by the plaintiffs.

To reanalyse the West Cumbria data, the plaintiffs needed recognized experts to perform the necessary work, and access to data held by the Medical Research Council (MRC) En- vironmental Epidemiology Unit at the University of Southampton (where Martin Gardner's team was based) and by BNF at Sellafield. Neither the MRC nor BNF was prepared to co- operate voluntarily in this venture. The plaintiffs, therefore, had to apply to the court for the release of the necessary information, to allow Stephen Evans, on behalf of the plaintiffs, to reanalyse the data using revised doses. This application was opposed by the MRC and BNF. Given the circumstances, that the plaintiffs required the release of these data to their expert to pursue the claim effectively, it was unlikely that a judge would have denied them access, and an order was made for the necessary information to be released confidentially to both parties.

Further, it was clear from correspondence between BNF and Martin Gardner which had been handed over in the discovery process that, since February 1990, Gardner and his colleagues had positively matched fathers to employment at Sellafield beyond those so linked in the original study. In addition, other queries had been raised by Gardner and his team in their efforts to improve the level of unambiguous linkage in the West Cumbria study. This work, part of the programme to extend the West Cumbria case-control study, was far from complete, and no results based on these extra data had been published. Nevertheless, the plaintiffs were anxious to use this additional information in their reanalysis of the West Cumbria data. They therefore again applied to the court for the release of the relevant data by the MRC and BNF.

This further application for data was also opposed by the MRC and BNF. The plaintiffs' application was supported in an affidavit by Stephen Evans and opposed in affidavits from me on behalf of BNF and Hazel Inskip on behalf of the MRC. (Martin Gardner had become seriously ill by this time, and the scientific interests of the MRC were represented by his successor, Hazel Inskip.) Much of the thrust of these affidavits was concerned with whether data obtained from an incomplete extension of the original study could have scientific validity. However, since the plaintiffs were arguing that it was imperative that this further data be made available to their expert, the court again ordered that the necessary information be released to both parties confidentially.

The defendants were then faced with a rather different situation from that pertaining at the outset. The central evidence was no longer to be the published results of the West Cumbria case-control study, or even a reproduction of these results produced by an expert acting for the plaintiffs, but the results generated from an analysis of an incomplete extended database, and using doses which could be quite different from those used in the original study. Given these circumstances, the defendants requested the court to order the MRC to make available to both parties those documents relating to the conduct of the West Cumbria study from its inception, so that details of the collection, collation and analysis of the data that were relevant to the paternal irradiation association could be examined by experts for preparing



320 R. Wakeford

expert evidence. However unpalatable, the reality was that, in the circumstances where the West Cumbria study was crucial to the plaintiffs' case, the defendants could not passively accept that no error had occurred in the design and execution of the study, and they asked for the opportunity for their experts to examine in detail the relevant documents. This application was granted by the court.

Thus considerable quantities of data held by the MRC and BNF relating to the (extended) West Cumbria case-control study were passed to a limited number of individuals involved on both sides of the litigation. Confidentiality was clearly an issue concerning the MRC and also BNF. To reconstruct occupational doses adequately, detailed work histories had to be generated and Sellafield employees who were already greatly concerned by the findings of the West Cumbria study were further troubled by the thought that personal information could be transferred out of BNF's keeping. As a consequence, names and means of identification had to be removed from MRC and BNF records before being used in the reanalysis, and an elaborate coding system had to be established by the MRC and BNF to enable the linking of workers to appropriate records. Strictly limited numbers of individuals in the MRC and BNF had access to the basis of these codes.

This episode illustrates the power of the legal process. Sufficiently motivated plaintiffs with the necessary financial and technical support, and the assistance of a recognized expert, were able to commit not only the defendants but also a third party, in this case the MRC, to be involved in an appreciable volume of work which allowed an extension and fresh analysis of a scientific study that had become the nub of the plaintiffs' case. Further, the defendants also required substantial information from the MRC relating to the way that the original study had been carried out, to satisfy themselves about the accuracy of the findings.

Some potential complications were resolved in that the occupational dosimetry experts acting for both sides were able to agree, after exchanging expert reports and much discussion, the preconceptional doses and their components for both Mr Reay and Mr Hope, and the Sellafield workers included in the (extended) West Cumbria case-control study. Also agreed between both sides was the content of the case-control data on which the reanalysis would be based, although the nature of the analysis was left open. The results of the reanalysis were presented in expert evidence for both sides of the litigation, although of course these results could be used only for the litigation under the terms of the court orders. As things turned out, the original association reported by Gardner et al. (1990) was broadly confirmed, although the extended reanalysis suggested that it was confined to cumulative paternal preconceptional dose (rather than the dose received shortly before conception) and leukaemia for the small minority of the offspring of the Sellafield workforce who were born in Seascale (see Parker et al. (1993), Health and Safety Executive (1993, 1994), Hodgson et al. (1994), Wakeford et al. (1994) and Little et al. (1994, 1996)). The argument, then, came to be centred on the scientific interpretation of the association.

At this time, considerable scientific work was under way which would have a bearing on the interpretation of the findings of the West Cumbria case-control study. Both sides, therefore, had to deal with a rapidly changing situation as new results became available. Relevant findings began to be published soon after the publication of the West Cumbria study, and this process continued right up until the end of the trial (and beyond). This substantially complicated matters for lawyers, experts and advisers alike.

5. The role of the expert

Potential expert witnesses are approached by solicitors acting for either the plaintiff or the




defendant because of their technical expertise in areas of relevance to the litigation. An expert is not obliged to become involved in litigation, except in the unusual circumstance of being subpoenaed. Having agreed to act, the expert prepares a written report on the area of evidence required by the lawyers. Although in an ideal world the expert's evidence would be completely impartial, in practice it is effectively impossible for the expert not to become, to some degree, emotionally involved with the position taken by either the plaintiff or the defendant, given the inevitable interaction between the expert and the lawyer. This has been discussed by Bowden (1995) and Bowden and Isted (1996). However, the expert should take care not to be beguiled by a persuasive lawyer to give evidence in an area in which he does not feel confident, since this is liable to be exposed during cross-examination. After all, it is the expert who will be questioned on his evidence in court, not the lawyer. At some agreed time before the trial (in the cases of Reay and Hope versus BNF this was in June 1992), the first tranches of expert reports are simultaneously exchanged, although sequential exchange does occur occasionally. The nature of a simultaneous exchange inevitably leads to a certain amount of guesswork concerning the other side's evidence. Owing to the need to respond to points made in the other side's reports, an expert is almost invariably required to produce at least one further written report. Some experts in the Reay and Hope versus BNF litigation were required to produce half a dozen reports to deal with the rapidly changing state of evidence, the later reports being submitted during the trial to address findings which had just become available.

Most expert witnesses are required to give oral evidence in court. At the time of the Reay and Hope versus BNF trial, this consisted of examination-in-chief by a barrister from the side for which the expert was appearing, followed by cross-examination by the other side's barrister, and finally re-examination by his own side. It is cross-examination where expert evidence is really put to the test, and which is, in general, most telling as far as the judge is concerned. The judge must not only arrive at a decision about whether or not the plaintiffs have proved their case, but he must also justify this decision in a reasoned judgment which must be based on the evidence put before him. If he errs in his reasoning, then his judgment can be the subject of an appeal to a higher court. Therefore, the judge must understand the expert evidence in appreciable detail and barristers go to considerable lengths in their presentation of the evidence, through their questioning of experts and in summarizing speeches, to ensure that this is so.

Cross-examination is a stimulating but sometimes harrowing experience. Top lawyers are extremely clever people, and those involved in the Reay and Hope versus BNF litigation had some of the sharpest intellects that I have encountered. The barristers with whom I worked had the unnerving ability to consume vast quantities of technical information, and then to regurgitate this information in a structured and most effective fashion for cross-examination. Very rarely did I find it necessary to prompt the barrister during his cross-examination of a plaintiff's expert, which was frequently highly detailed.

In general, an expert will give oral evidence in court during two 2-hour sessions per day, and this questioning could extend over several days. If an expert sticks to the area of his expertise and does not overextend himself, then, because he is the expert, the experience of cross-examination, although challenging, can be invigorating. However, woe betide the expert who through arrogance or ignorance thinks that he can intellectually outmanoeuvre the cross-examining barrister who will usually have years of experience in questioning witnesses in many complex areas of evidence. I have seen several expert witnesses suffer greatly during cross-examination because they ventured into territory beyond their expertise, spoke with insufficient knowledge on particular studies or attempted to persist in a line of



322 R. Wakeford

reasoning which could not be sustained. Unlike the seminar, during cross-examination the awkward questions will not go away. The structured questioning of a well-briefed barrister can be a searching and rigorous examination of scientific evidence and inference, and is an extremely effective way for the judge to come to appreciate what the evidence can and cannot support.

It was unfortunate that Martin Gardner and his colleagues became involved through no desire of their own in the Reay and Hope versus BNF litigation. It is even more unfortunate that Hazel Inskip, who joined Martin Gardner's group after the publication of the initial results of the West Cumbria study, had to put so much time and effort into the supply of data to both sides of the litigation on the instructions of the court. Those scientists conducting and reporting research in the area of public health should always bear in mind, particularly if the results are controversial and could be the subject of litigation, that, in cases of personal injury, effectively the entire record of their study could be scrutinized in great detail by external experts acting for both parties in a legal action and their analyses could be repeated. As one of those who had access to the West Cumbria study data for the litigation, I have to say that I was impressed by the standard of the records kept by Martin Gardner and his colleagues. Nevertheless, it is almost inevitable, on detailed scrutiny of a complex study such as the West Cumbria case-control study, that certain aspects and decisions are open to criticism. This did occur during the Reay and Hope versus BNF litigation, and has been outlined elsewhere (Wakeford and Tawn, 1994). These criticisms, detailed in expert reports before the trial began, were neither trivial nor malicious but material to the interpretation of the association which was the central issue in the litigation. They were contested by Martin Gardner in a written statement but supported by the defendants' experts and sustained under cross-examination, and the judge broadly accepted their validity, although he also considered that the West Cumbria study was, overall, 'a good study, well carried out and presented' (French, 1994).

In the end it was the isolated paternal preconceptional dose association, viewed within the broad context of scientific evidence, which led to the outcome of this particular litigation. Interestingly, in his interpretation of this epidemiological association, the judge relied heavily on the guidelines set out by Hill (1965) which he regarded as 'an attempt to systematise common sense' (French, 1994). In his comprehensive judgment, the judge concluded (French, 1994)

'On the evidence before me, the scales tilt decisively in favour of the Defendants and the Plaintiffs, therefore, have failed to satisfy me on the balance of probabilities that PPI [paternal preconceptional irradiation] was a material contributory cause of the Seascale excess or, it must follow, of (a) the leukaemia of Dorothy Reay or (b) the NHL of Vivien Hope. . . . In the result, there must be Judgment for the Defendants.'

The plaintiffs did not appeal against this decision, and a second tranche of cases (which included claims of a similar nature relating to the UKAEA's historical operations at Dounreay) was 'struck out' in a subsequent hearing on the basis that, in the light of the judgment in the Reay and Hope cases, they had no prospect of success.

A detailed review of the scientific issues dealt with in the Reay and Hope versus BNF cases has recently been published in the fourth report of the Committee on Medical Aspects of Radiation in the Environment (1996), which discusses the Seascale childhood leukaemia excess and possible causes, including radiation exposure due to operations at Sellafield. Those seeking reassurance of the correctness of the judge's decision can find it in the opinion of this scientific 'jury'.




6. Conclusions The legal cases of Reay versus BNF and Hope versus BNF graphically illustrate the interaction between science and scientists and the law and lawyers. Not only are the results of scientific studies used to support or refute a claim, but also, under circumstances where a single study plays a paramount role in a personal injury case, the whole structure of the study from proposal to publication (and beyond) can be scrutinized by lawyers and experts acting for both parties using the study records held by the researchers. This is so even though those scientists who were responsible for the study may not be directly involved in the litigation. Those carrying out research, particularly on high profile and contentious issues, should keep in mind the possibility that their procedures could undergo detailed examination for litigation. Failure to comply with a court order requiring the release of such data would be contempt of court and would have serious consequences for those controlling the data.

Scientists may be approached by solicitors to act as expert witnesses or technical advisers. Some may not feel comfortable in such a role, or feel that it would present them with a conflict of interest. Others may feel that they have a duty to society to give the court the benefit of their expertise. What is clear is that a scientist who decides to act as an expert witness should not approach this lightly. An epidemiologist, in particular, must understand the basis of the claim being made and be satisfied with the position being taken by the side for which he is to act. He must anticipate that the evidence which he gives will be subjected to detailed scrutiny during cross-examination, and he should not underestimate the abilities or knowledge of the barrister questioning him. Cross-examination can be likened to a hostile viva voce and cannot be expected to be easy, but it does provide an effective means of testing the evidence. Scientists are obliged to disseminate their knowledge more widely than the scientific community, and Smith (1996) has argued that the discipline of statistics is 'vital to the honest and decent conduct of public affairs'. The provision of expert evidence to the law courts is part of this process. Interaction with the law, however, should be treated just as seriously as the more usual duties of a scientist.

It is inevitable and, indeed, highly desirable that scientific evidence will continue to be relied on by the courts. Sometimes evidence can be agreed between the two parties and clearly this should be achieved whenever possible, but, where major differences of opinion exist, cross-examination appears to be the most effective means of determining the position that is best supported by the evidence. That scientifically contentious issues will continue to give rise to legal claims is exemplified by allegations that exposures to extremely low frequency electromagnetic fields, such as those associated with electrical power lines and appliances, have caused childhood leukaemia, even though a consensus on the scientific interpretation of the epidemiological evidence on this subject has yet to be achieved. Again, the validity of such claims would be determined on the basis of the scientific information that is available as expert evidence at the time of the trial. Experts must be willing to understand, and to operate within, the legal framework used to decide the outcome of personal injury claims like these. I hope that this paper will provide at least some illumination for the scientists and statisticians who become involved in civil litigation, and for the many more who watch with interest from the side-lines.

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Documents

Epidemiology and Litigation--The Sellafield Childhood Leukaemia Cases