Providing a Forensic Expert Opinion on the “Degree of Force”: Evidentiary Considerations

SIMPLE SUMMARY: When giving evidence in court, forensic pathologists and anthropologists are often asked for their opinion on the amount, or degree of force required to cause a specific injury. Such ‘degree of force’ questions are considered difficult, if not impossible to answer due to many theoretical and practical issues. This paper explores these issues and provides a possible solution. First, the logical underpinnings of the question on the ‘degree of force’ are explored. Then the experimental research on ‘degree of force’ is reviewed and the limitations with applying this research to everyday forensic casework are discussed. In the second part of the paper, it is argued that these limitations do not, however, mean that a forensic pathologist or anthropologist cannot add anything of value to the discussion. The application of Bayes’ theorem helps to circumvent many of the problems. The final part of the paper is dedicated to a detailed discussion of how it can be applied to the issue of ‘degree of force’. ABSTRACT: Forensic pathologists and anthropologists are often asked in court for an opinion about the degree of force required to cause a specific injury. This paper examines and discusses the concept of ‘degree of force’ and why it is considered a pertinent issue in legal proceedings. This discussion identifies the implicit assumptions that often underpin questions about the ‘degree of force’. The current knowledge base for opinions on the degree of force is then provided by means of a literature review. A critical appraisal of this literature shows that much of the results from experimental research is of limited value in routine casework. An alternative approach to addressing the issue is provided through a discussion of the application of Bayes’ theorem, also called the likelihood ratio framework. It is argued that the use of this framework makes it possible for an expert to provide relevant and specific evidence, whilst maintaining the boundaries of their field of expertise.