JUDGING BETWEEN CONFLICTING EXPERT EVIDENCE

Date01 December 2014
Published date01 December 2014

Understanding the Scientific Method and Its Impact on Apprehending Expert Evidence

A proper understanding of the scientific method would impact the way that the law and the courts should apprehend expert evidence (including evidence on fields of knowledge other than science). In this article, the author examines various possible types of conflicts of expert evidence and the different approaches that the Singapore courts have taken in respect of such conflicts. It is argued that where there are conflicts over methodology or theory, the courts should consider whether there are demarcations of dominant and subordinate paradigms of methodology or theory and whether there is sufficient justificatory force in rebutting the dominant paradigm; where there is no clear dominant paradigm, the courts should rely on neutral reasoning processes such as the burden of proof. It would be observed that the above principles were applied by the High Court in Tan Eng Hong v Attorney-General[2013] 4 SLR 1059.

I. Introduction

1 What happens when a judge is presented with conflicting or inconsistent evidence from two or more experts? Would it not require a “super-judge” who possesses the relevant specialised expertise and knowledge to assess the expert opinions and thereby prefer one over the other? A century ago, Justice Learned Hand had elegantly framed this problem thus:1

… the whole object of the expert is to tell the jury, not facts … but general truths derived from his specialised experience. But 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 the expert is necessary at all.

2 Judges are often presented with evidence on matters that are beyond their field of expertise and knowledge, ranging from the

medical-scientific to foreign law. Such scenarios present a tension between the need for a final and conclusive determination of parties' dispute and rights, and the need for “rationality” in adjudication, without which the legitimacy of the adjudication would be undermined. An additional problem is that the expert witnesses obtained by parties are ultimately “hired guns” and thus susceptible to offering “biased” opinions.2 This adds further pressure on judges to discern truthful expert opinion from partial ones. Faced with such a predicament, we could be resigned to the conclusion that there are presumably no manageable judicial standards and thus accept that such disputes are not justiciable (to use the term loosely), or we could find practical solutions to achieve the best possible outcome.3

3 This article begins by considering the nature of the scientific method and the various normative rationales at play with regard to the problem of conflicting expert evidence. Following that, the author shall analyse the four types of conflicts: (a) conflict over assumed facts; (b) conflict over diagnosis or analysis of facts; (c) conflict over methodology; and (d) conflict over theory. With regard to the former two types, no specialised expertise on the part of the courts is required for adjudication. For the latter two, it shall be argued that where there is a demarcation of dominant and subordinate paradigms of methodology or theory, the dominant paradigm would hold presumptive weight unless the party seeking to rely on the subordinate paradigm establishes sufficient justificatory force to rebut the presumption, in which case the court should not prefer the “dominant paradigm” expert evidence; where, however, there is no clear dominant paradigm, the court should rely on neutral reasoning processes such as the burden of proof. This proposed approach would allow the court to rationally and legitimately adjudicate between conflicting expert evidence without pretending to be a “super-expert”, while ensuring the pursuit of the ends of justice in each case. The author now turns to consider the nature of the scientific method and explain why expert evidence should be apprehended critically in light of the former.

II. The nature of the scientific method

4 Science and law have enjoyed an intimate relationship since long ago. Already in the 16th century, medical and philosophy professors

of Leiden University were asked to provide an answer to a controversial legal question of that time: whether the cold water test was adequate to prove witchcraft. The professors testified that the test was completely inadequate for that because humans naturally float on water.4 Today, much criticism has been levelled against jurists for not taking into account developments in the philosophy of science, ie, that science is no longer seen as capable of finding absolute truth.5 One consequence of the law's failure to catch up with science is that often, when scientists offer conflicting evidence, the uncritical response is given that some of the disagreeing scientists are dishonest or unreliable.6 Yet, this is premised on a misconceived view of science. The following survey of the historical development of the philosophy of science would explicate this.

5 During the 17th century, Isaac Newton introduced a paradigm of science based on observation, experiment and induction. This became the dominant view of modern science. Newton's work influenced the philosopher, John Locke, who asserted that all propositions had to be ranked on a scale of probabilities to determine their weight, the level of probability being proportionate to the quality and quantity of evidence. Locke thus rejected the rationalists' notion that man's capacity to understand knowledge rests upon certain maxims of reason. Locke's philosophy would have a significant impact on evidence law.7

6 From the heritage of Newton and Locke birthed logical positivism, which held sway up to the early 20th century. Its central tenet is that scientific facts are objective and accurately describe the facts of the world as they are. This is because science relies only on observable phenomena from which general principles are induced; these principles are then verifiable by conducting experiments. Therefore, any hypothesis not founded on and verifiable by observable phenomena would not be deemed scientific knowledge, ie, absolute truth.

7 However, in 1935, Karl Popper, influenced by the scepticism of David Hume, challenged logical positivism with a philosophy of “critical

rationalism”; in particular, he critiqued logical positivism's emphasis on induction and verification.8 He argued that the proper empirical method to acquire knowledge was not verification but falsification. This means that, no matter how many singular observations, one can never derive universal, generalisable truth from the particular, even if the present observations have always resembled the past observations.

8 Another robust philosophy of science was brought to prominence in 1962 by Thomas Kuhn,9 who argued that every scientific theory had anomalies. If every anomaly was a ground for rejecting a theory, every theory ought to have been rejected all the time. If, otherwise, only “severe anomalies” would justify rejection of a theory, then there should be some criteria for improbability or degree of falsification. In the history of science, science usually uncovers new and unsuspected phenomena, ie, anomalies; such an anomaly would not cause the rejection of a dominant theory until the anomaly is deemed to be more than just an anomaly. When the anomaly is studied and a competing paradigm emerges, it may then gain more widespread acceptance until it becomes mainstream as the dominant paradigm of science. That is, until another anomaly is uncovered and this cycle is repeated with regard to the new anomaly. The selection and rejection of scientific theories are neither a matter of rationality nor even determined on evidence. Instead, the determination is based on some level of subjectivity and philosophical premise.

9 A similar view was also pronounced by Patricia Huisman.10 Huisman argued that rationality and critical debate does not guarantee the exposing of subjective influences within scientific research, because these influences may already be institutionalised as values within the scientific community. There have been and always will be differing views of science, eg, an anarchistic theory of the philosophy of science.11

10 The debate on the nature of the scientific method continues till today. Yet, the above brief survey of the historic developments in the philosophy of science suggests that scientific propositions are merely interpretations of observations within specific contexts and that achieves status of fact through social acceptance within a scientific community. Scientific knowledge is therefore said to be social knowledge. Scientific truths are today generally no longer deemed as absolute truths, but contingent and debatable.12 If indeed the scientific method, which was once deemed to produce the most accurate, objective and certain findings of fact, is now impinged, needless to say, most other fields of knowledge (eg, social sciences, the arts, etc) suffer the same criticism. That is not to say that there can never be any certainty. Instead, scientific study and any other form of study might still be meaningful if spoken of in terms of degrees of probability or meaningful certainty.

11 This has wide-ranging implications. It has thus been said that:13

… the rejection of a simple dichotomy between ‘good’ and ‘bad’ science facilitates discussion in a number of areas otherwise precluded. For instance, questions relating to the efficacy of various sciences, their objectives, and the ethics of their practitioners can be examined in more specific local terms, freed from the need to anchor them to over-arching, unworkable, mythological images of science.

A critical perspective of the nature of science has significant impact on the litigation process. The wrong perception that science...

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