Admissibility of Expert Evidence in Criminal Proceeding

Introduction

Rabelais’ Judge Bridlegoose lays down a challenge for the legal profession. Bridlegoose threw dice to decide cases his deductive logic being that by using dice both sides had an equal chance of winning and therefore over the long run he would get the ‘right’ result in about half the cases^[1]. A number that given the “arbitrary confusion, the obfuscation and chicaneries of lawyers and the possibilities of his own fallibility there was no such guarantee he would achieve this level”^[2]. All serious theoretical discourse on the Law of Evidence mandates ‘rectitude of decision’^[3] so the challenge is to get a better rectitude of decision in both design and practice than would be achieved by throwing dice. The scandals in recent years surrounding the cases of people such as Angela Canning^[4] and Sally Clarke^[5] and the overturning of convictions based on expert medical evidence have exemplified a classic example of a failure to get rectitude of decision; if their judgement had been based on the roll of a dice their results may have been fairer to them. The issue of expert evidence and its relationship to the exclusionary evidential rules on opinion and hearsay has been the subject of a large academic scrutiny and it is to this subject matter that this work will be focused upon.

The dangers of expert evidence are well rehearsed in the courts and it is a very contentious area, the well known dicta of Lawton LJ in the case of R v. Turner^[6] exemplifies an ancillary point to the one made above, veracity is to be determined by the decision maker and we must become wary of abrogating such a right and stated that English law had to be wary of becoming too deferential or reliant on expert evidence because it is trial by judge and jury not by expert. The issues which this work seeks to deal with can be of the utmost importance, in this work I hope to critically assess the current state of the law as regards expert evidence post-Criminal Justice Act 2003^[7]. The work attempts to fuse the two themes that I have implied here namely; the current attitude to expert evidence vis a vis the inherent conceptual dangers of the subject matter and secondly, whether as a whole it deals with the aims of the Law of Evidence more generally. Its position as an exception to such a large rule as Hearsay makes this Janus-like approach^[8] necessary and lends considerably more conceptual clarity in a subject area which is contentious for various reasons with rich intellectual backgrounds.

We will start by looking at a history of the evolution of the concept of expert evidence as an exception to the exclusionary rule against opinion evidence which will combine both elements of practical law and theoretical background justifications for the existence of such laws. This section will be the bulk of the essay as we seek to build an in depth account of Expert Evidence and will look at a number of issues such as the courts attitude to new technologies and the detailed case law about the areas upon which the courts will allow expert evidence, always evaluating this against the background purposes of the rule. The evaluation in this section attempts to assess whether the rules on expert evidence exhibit a holistic coherence. This neatly flows into the second part of the work which will discuss expert evidence as an exception to the hearsay rule. In conclusion, I will draw both strands of the work together and propose a number of tentative amendments, however whilst this is a critical work, as we shall see the complicated nature of all the issues requires us to go into great detail about a large number of issues. The nature of this work is about criticising the lack of holistic treatment of the subject matter rather than substantive reforms.

Philosophy of Expert Evidence

The jurisprudential treatment of the law of evidence has a long history and it would be impossible in this section to do justice to the variety and complexity of the jurisprudential arguments that surround this subject matter. However as we shall see Expert Evidence is a particularly interesting subject because of its position in the Law of Evidence.

The general law of evidence in the Anglo-American system is built on a system of free proof with a number of exclusionary rules. This picture is very neat and easy for us to deal with on a conceptual basis. There is a clear need for any decision-maker to have all the available facts before him so that he can make the correct, or just, decision. However, some evidence is inherently misleading, unreliable and prejudicial. The individual rights of the parties and the demands of justice in the Anglo-American system mean that this evidence is excluded so that in effect the decision-maker makes his deliberations on all the ‘best evidence’ available at the time. The Adversarial trial system is the best way of eliciting this information from the available sources such as witnesses and real evidence. This is the prosaic understanding that underlies to a large degree the modern day criminal justice system.

However, the situation becomes more difficult when evidence doesn’t neatly fall into the reliable / unreliable category. Furthermore it can cause confusion where generally unreliable evidence is admitted in certain cases because of unique concerns. Expert Evidence is precisely one of these types. We will discuss these issues in greater detail below however we will give a brief overview at this point. The reasons for including expert evidence are self-evident to a point, it is a rare judge who believes he understands absolutely every piece of information that he may be presented with. The average judge may have very little grasp of the scientific probability ratio’s that underlie DNA evidence or the minutiae of the refractive index of glass. However, these issues can be central in a trial and it is thus essential if justice is to be done that a judge understands the evidence. The problem is that much of scientific advice will be opinion based, furthermore science is generally accumulative and thus inevitably there will be a degree of reliance on the work of academic peers. These attributes cause all expert evidence to fall foul of two large exclusionary rules of evidence: Hearsay and Opinion evidence. The situation thus becomes highly complex because there is an inherent tension between the principles that state such evidence is unreliable and the perhaps more fundamental principles that require any decision that may deprive an individual of liberty or property to be based on a rational and cogent basis. As we continue we will see that these principles are the guiding principles for the judiciary and that the substantive law that govern the admissibility of expert evidence embody such principles. However, their position as an exception to the rule also place an inherently contra proferentem approach whereby the courts are likely to construe the meaning of such exceptions narrowly. The inconsistency between the rules highlights a further dimension; that overall the philosophy that is guiding the growth and formation of law in this respect is far from clear.

Opinion Evidence and Its relationship to Expert Evidence

Mr Smeaton understands the construction of harbours, the causes of their destruction and how remedied … I have myself received the opinion of Mr Smeaton respecting mills, as a matter of science. The cause of the decay of the harbour is also a matter of science … Of this, such men as Mr Smeaton alone can judge. Therefore, we are of the opinion that his judgment, formed on facts, was proper evidence

• • Lord Mansfield, Folkes v. Chard (1782) 3 Doug KB 157

The issue of expert evidence is fundamentally based on practicality and common sense, unfortunately it suffers from the common deficiency of such concepts; it is incredibly difficult to translate such a nebulous concept into prescriptive rules of law. The problems associated with the concept will become apparent as we continue this discussion but just as this point I want to make clear the critical model that I’m using to assess the law in this area as it makes a large impact to the direction of the whole work. Lord Mansfield above pointed out that the evidence was taken as science and therefore as objective, these criteria for why we accept evidence are not exhaustive and as we shall it is a highly varied concept.

Frederick Schauer has written on a particularly interesting aspect of legal rules that examines the correlation between the background moral, social &c… and their translation into law. Schauer hypothesises that in a society where all the people agreed on the content of moral principles there would still be a problem over the conversion of these moral principles into coercive and authoritative social rules i.e. Law^[9]. This is because for such rules to be authoritative they must be formal and strictly applicable and actually supplant moral principles^[10]. However because these rules are…

‘…promulgated by human beings of finite reasoning & informational capacities & that are meant to improve the moral condition of human beings of finite reasoning and Informational capacities will always fail to capture precisely the requirements of morality’

It is this so called ‘asymmetry of authority’ that this work is going to be sensitive to for the first section, the distinctive needs and justifications for expert evidence as compared to the letter of the law. It is, as stated above, highly improbable that given our finite reasoning that the law is wholly satisfactory therefore the aim is merely to assess whether the rules are under or over-inclusive as regards the justifications that we will discuss in this work. I mention this here so that the reader is fully aware of my aims at the outset.

The common law ban on opinion evidence except in the case of experts is generally traced to Lord Mansfield’s dicta in the Folkes case, above, however the recognition by society that in some cases the use of experts can be an aid to the arbitration of justice dates to significantly earlier. Hodgkinson^[11] cites the 14^th century case about mayhem which is mentioned in Buckley v. Rice Thomas^[12] as an early authority whereby surgeons where summoned to assist the court as to whether particular wounds constituted mayhem or not because the judges lacked the requisite skill to reach a conclusion. In Buckley Saunders J made an obiter dicta remark which summed up one of the main justifications for admitting expert evidence at the time:

‘If matters arise in our law which concern other sciences or faculties, we commonly apply for the aid of that science or faculty which it concerns, which is an honourable and commendable thing in our law’^[13]

However, at the same time as this the law was woefully inept to cope with some of the more subtle distinctions that exist within our modern day legal framework. When we realise that certain evidential rules developed much later, for example at the time of Buckley an accused was not even allowed to have witnesses or even a proper defence to a murder trial. These rules developed over time and the eminent evidence scholar John Wigmore has argued that importantly for the issue of expert evidence the willingness of the courts to rely on expert evidence was very much unguided by any formal principles until the distinction between opinion and factual evidence became more formed^[14]. The understanding of the interrelationship between expert evidence and the exclusionary rules on hearsay and opinion evidence becomes at this point, the early nineteenth century according to Wigmore, vital.

On a reading of the older sources prior to the advent of this distinction the courts have no clear principles guiding them. This is not per se a bad thing because it is arguable that later distinctions, particularly driven by the scientific approach to law taken by enlightenment scholars such as Bentham and Wigmore have, in the light of modern day post-modernist and realist critiques, lost much of their poignancy. However, the distinction between opinion and fact is dominant in the jurisprudence of the courts and is a very traditional part of the law of evidence. The justifications given for this ban on opinion evidence are traditionally four fold^[15]; primarily the opinion of non-expert usurps the function of the jury and could lead to an undue influence being exerted by the witness on the jury members, this was pointed out by Vaughan CJ in Bushell’s Case^[16]:

‘The Verdict of a Jury and Evidence of a witness are very different things…a witness swears but to what he hath heard or seen, generally or more largely, to what hath fallen under his senses. But a Juryman swears to what he can infer and conclude…’^[17]

Another reason is that opinion evidence is largely irrelevant, which makes common sense when we think about the situations in which the rule operates. It is irrelevant if a non-expert opinion is given on an area requiring expertise as that person simply does not have the substantive knowledge to back-up an assertion of opinion. Furthermore if an opinion is given where no expertise is needed, quite apart from the prejudicial effect it may have, it is irrelevant as the decision maker is perfectly capable of forming their own opinion on the facts. Thirdly, a witness cannot be prosecuted for perjury as regards their opinion, or liable in tort for negligence^[18], the law therefore doesn’t provide for any safeguards on the veracity of witness opinions. Finally, there is an established fear that the proffering of an opinion might circumvent other exclusionary rules such as relevance, hearsay and the findings of other tribunals^[19]. The last justification appears to lack a degree of poignancy because the other exclusionary rules are widely known and therefore an opinion can be treated just like any other item of evidence and be excluded if it falls under those exclusions.

The impact of this distinction was revolutionary when it started to infuse legal practice in the 19^th century^[20] because before the fact / opinion divide was understood and substantive laws developed to represent such concerns, the use of expert witnesses was an ‘aid’ to the court that was where the reflection ended. The opinion / fact divide means that expert witnesses become an exception in their own right and thus identifiable as a particular class of evidence. This subtle change in perception means that the internal justifications of exception evidence come into play. They are an exception to a general rule and therefore the admittance of expert opinion has to be more strictly understood and that is why we see a lot of case law, in the late nineteenth century and twentieth century, that begins to flesh out the jurisprudential and substantive dimensions of the exception as awareness of the competing concerns in this area begin to infuse the judiciary.

In discussing the justifications for the expert witness exception Hall & Smith describe the overall approach that the court takes to the exception as being a rule that ‘opinion of scientific men upon proven facts may be given by men of science within their own science’^[21]. However the tension between expert evidence and opinion evidence is exhibited in how that overarching principle is translated into law. The purpose of the following sections is to show how the basic tensions that exist in the above internal justification give rise to different problems. An understanding of the basic justification given for using experts is immeasurably useful and ought to be borne in mind; we may well be critical in the way that the need for experts is translated into substantive law but at no point are we critical of the de facto use of experts.

1. Contradiction of Expert Evidence Law

Hodgkinson refers to there being a contradiction at the centre of expert evidence which can be clearly understood when we think out the problem logically^[22]. Opinion evidence is predominantly excluded for its prejudicial effect and usurpation of the role of judge and jury, as we shall see below. The various exceptions for experts are complicated but they represent a mix between the common law reservations over opinion evidence and the need for aid in fields of expertise that it is impossible for judges and juries to make an informed decision upon. However when contradictory expert evidence is placed before the court, both of which have equal validity because of their backgrounds, the court is back in square one, as the great American judge and jurist Judge Learned Hand stated:

‘How can the jury judge between two statements each founded upon an experience confessedly foreign in kind to their own? It is just because they are incompetent for such a task that an expert is necessary at all’^[23]

The main culprit in these circumstances is the adversarial system as Davies points out:

‘If we were to…to design a system for the resolution of questions involving expertise, we would probably start with the idea that an expert, or a panel of experts, should decide such questions. If someone were to suggest to us…a person who had no expertise would decide such questions after hearing competing arguments from opposing experts, we would dismiss it as bizarre’^[24]

There are a number of reasons why the contradiction in expert evidence is symptomatic of the flaws of the adversarial system. Primarily the dichotic straightjacket that such a system forces on the presentation of evidence, especially in criminal procedure, is not suited to the presentation of scientific arguments, many do not admit of conclusive answers and cannot be wholly presented as supporting one party’s narrative. Nevertheless a retained expert may suffer from what is called the adversarial bias^[25] whereby they’re encouraged to expand on the evidence that supports one side’s narrative. This practice in itself exacerbates the contradiction of expert evidence, Davies quotes an Australian judge who referred to two cases where scientific knowledge was required and two diametrically opposed scientific opinions were given^[26], the quandary this leaves for the judge is two-fold. The judge or jury must assess to what extent the evidence being presented is the result of adversarial bias and what is the whole picture, the more complicated the problem the more difficult this inevitably becomes. Secondly, the judge has to come to a decision which is right and therefore requires more than anything an independent expert to help them again the need will be greater in situations of greater complexity. When we consider the general demographic of the judiciary in most cases being those well into middle-age and consider that, especially in cases of Intellectual Property, they may fall to consider some advanced technological concepts which would be wholly alien to their general education then we can see how difficult the situation may become.

There are a large number of potential solutions to these problems none of them are ideal however for our purpose the mere realisation of the dimensions of this problem are what is important. The justifications and competing arguments that we will discuss regarding prejudicial effect, aid, justice &c…which inform the main common law principles of expert evidence all have problems or distortions when they are translated into practice. This problem is one of many with the expert witness system because it means that the very reason for the exception to the exclusionary rule on opinion and hearsay is undermined. If the adversarial system causes expertise to be cancelled out then given the time, expense and potential injustices that can arise perhaps they are not the aid to the courts that they once were. If their opinion is known to be diametrically opposed by a similar expert then their opinion is as good as the judges’ or jury members’ and as they can be no aid, consequently they are frivolous and potentially prejudicial.

2. Ultimate Issue & Information in the Public Domain

The Expert Opinion must be based upon the facts, if there is an error as to the facts then the Expert may not, however skilled, give his opinion on the issue^[27]. The opinion is considered to be ‘valueless’^[28] in the same ways as normal opinion evidence. The opinion proffered also has to be necessary in order to aid the understanding of the decision-maker in a particular case. A good comparison can be made in this respect between DPP v. Jordan^[29] and DPP v. AB & C Chewing Gum Limited^[30] because these cases both revolved around the impact of obscene publications on people. In the Jordan case the court upheld the ideology that jurors were able to make up their own minds and did not need expert psychological evidence as to the effect of obscene materials:

‘They cannot be told by the psychologist or anyone else what the effects of the material might be…since the decision has been given to the jury as representing the ordinary man, it follows that, as matters affecting the ordinary man, the jury, as such, must make it’^[31]

This approach has debarred certain types of evidence, one such type of evidence, which was paradigmatic until recently^[32], is that of expert evidence as to witness credibility. This approach is not unanimously supported for example in Scotland there are a number of cases and articles on the issue. Raitt^[33] has suggested that in certain cases there is considerable doubt over whether or not a typical juror or judge can understand the issues that may effect witness credibility. The examples that she gives is victims of domestic abuse and victims of child abuse, the nature of these crimes and the potential psychological effects on a witness are potentially completely alien to the experience of most jurors and judges^[34]. In R v. Turner the court laid down the reasons why such evidence ought not to be admitted:

‘authority for the proposition that in all cases psychologists and psychiatrists can be called to prove the probability of the accused’s veracity. If any such rule was applied in our courts, trial by psychiatrists would be likely to take the place of trial by jury and magistrates’^[35]

The courts have now reconsidered that the science is now stable enough and as we shall see the intermingling between this issue and the issue of reliability is quite large. The development of this rule in comparison to some of the continental jurisdictions gives us an interesting comparison of the underlying motivations in the UK system. The judge in both South Africa and other civil law jurisdictions posit the judge as the ultimate trier of fact so the test laid out in Turner as to the admissibility turning on the helpfulness is treated more literally. The judge asks whether this or that piece of expert evidence would truly be of use to him in coming to a decision in the particular case. However, as we have seen above the concern of English law is not so much on a strictly ‘helpful’ basis because it is interpreted to have more to do with the Ultimate Issue rule that we will discuss below. This means that there is an emphasis on the normal / abnormal sphere divide^[36] and the judges sit as arbiters of that divide. The arbitrary nature of this divide has been questioned using similar studies to that of Raitt, above, and the point has been made that ‘much common behaviour is ‘demonstratively counter intuitive in the sense that “ordinary men and women” generally misunderstand [it]’^[37].

In A,B &C the court considered another prosecution under the Obscene Publications Act 1959 similar to Jordan however as the target audience was children rather than adults, psychological evidence was allowed because ‘any jury and any justices need all the help they can get’^[38] when it comes to children. Lord Wilberforce commenting on the nature of the distinction in Jordan stated:

‘To this general rule there may be an exception in a case where the likely readers are a special class, such that a jury cannot be expected to understand the likely impact of the material upon its members without assistance. In such a case evidence from persons qualified by study or experience of that class may be admissible’^[39]

This kind of distinction is seen across the board as regards expert evidence and forms a wider rule that the opinion of an expert is not necessary or helpful where there is not some identifiable body of science which is not considered to be understandable by the average person^[40]. In R v. Masih^[41] the court specifically stated ‘in order to enlighten the jury upon a matter which is abnormal and therefore, ex hypothesi, presumably outside their experience’ then expert evidence will be allowed. The decision is one of pure discretion and a systematic study of what is allowable would be almost obsolete by the time it was written because of the variation in what is considered in the public domain. Zuckerman specifically states on this issue:

‘A judge deciding whether expert opinion should be accepted as an arbiter of a certain matter has to consider the state of public opinion on the point. If the community has come to defer to professional standards on the matters in question, the courts will normally follow suit’^[42]

This issue will become more pertinent later on when we discuss the courts attitude to new technologies and medical evidence. The law has exhibited a degree of incoherence and particularism in its application of the normal / abnormal divide which is, as we stated, inherently likely to occur because of its discretionary basis. In R v. Lowery^[43] which allowed psychological evidence in the case of two adults, on the face of it this seems to be contrary to the decision in Jordan above and the general rule against having expert evidence on an area considered in the public domain. In that case Lord Morris justified his admittance of such evidence by stating ‘When an accused person put his character in issue, he is in effect asking a jury to take the view that he is not one who would be disposed to have committed or would be likely to have committed the crime in question… if an accused person is not of good character, the law has been firm’^[44]. This tenet of the law has become one that centrally justifies the existence of the rule, the expert’s role has always been one of ‘aid’ since its very inception however that aid is circumscribed to fall only in those categories which the court decides it requires such aid. However, the tension between the aid an expert opinion can give the court and the perceived potential prejudices of such aid mean that the law goes onto circumscribe the role of an expert.

The distinction that Lord Wilberforce was making in Jordan is significantly related to the more fundamental rule that Expert Witnesses cannot give evidence on the ‘ultimate issue’. This concept is very vague but is a product of both the tension I mentioned above between the expert evidence exception and the general rules of evidence as well as the potentially determinative weight that will be given by a lay person to such evidence. The basic premise of the ultimate issue rule is that the expert shouldn’t give an opinion on any issues which it is for the judge or jury to decide, the classical position was outlined by Cresswell J in National Justice Compania Naviera SA v. Prudential Assurance Co Ltd^[45] where he remarked that ‘An expert witness should provide independent assistance to the Court by way of objective unbiased opinion in relation to matters within his expertise’^[46]. The idea of ultimate issue is perhaps best understood by use of an example.