Demonstrating reliability through transparency: A scientific validity framework to assist scientists and lawyers in criminal proceedings.

In recent decades, forensic science evidence has come to play an increasingly significant role in criminal proceedings. However, the ability of non-scientists (lay-persons, including lawyers and judges) within criminal justice systems to recognise and resolve issues of validity and reliability relating to expert opinion evidence has not maintained pace with the need to do so. Despite international scrutiny from scientists, statisticians, governments and those involved in law reform, the parameters of a) different forensic disciplines and b) some case specific interpretations, remain elusive to some legal practitioners and judges. It is therefore essential that within the context of national, and increasingly international and transnational criminal investigations, forensic science experts convey the evidential value of the scientific findings in a manner that is understandable to, and useable by all. To assist, this paper first identifies the organisational structures necessary to scaffold and support the delivery of reliable expert opinion evidence. This is followed by a format for transparently reporting the reasoning and the scientific validity underpinning the expert's evidence within their report: a tripartite Scientific Validity Framework. This framework is comprised of (i) foundational validity, (ii) applied validity and (iii) the new concept of evaluative validity. Such a framework, because of its underlying scientific principles, is applicable to expert reports in any jurisdiction and is complementary to different national approaches. That is because utilising this framework could ensure that experts can, and do, demonstrate that their case-specific opinion is reliable and alert the legal profession to the expert's reasoning process and any limitations in the scientific validity underpinning the opinion.