Was It Wrong to Use Statistics in R v Clark? A Case Study of the Use of Statistical Evidence in Criminal Courts

Abstract

This chapter discusses the use of statistical evidence to prove the material fact of causation in criminal courts. It focuses on R v Clark, in which a mother was wrongfully convicted of murdering both her babies. In order to disprove a potential defence claim that the babies died of SIDS (aka cot death), the prosecution adduced statistics that allegedly showed that the probability of two SIDS deaths in a family similar to the Clarks was 1 in 73 million. This chapter considers the question of whether it was wrong to use such statistical evidence in Clark. Four common explanations of why it was wrong, each of which attributes the wrongful convictions to the use or misuse of the statistical evidence, are scrutinised and rejected. However, drawing on the theory of contrastive explanation, it is argued that it was still wrong in principle to use the SIDS statistics in Clark, because using them properly would require another piece of evidence which is clearly objectionable: statistical evidence on the rate of smothering among mothers who are similar to Clark. Regardless of whether the exercise of comparing probabilities of SIDS and smothering is feasible, such an exercise should not be conducted as part of criminal proceedings. This chapter thus concludes that Clark should serve as a warning against any attempt to prove the fact of causation using statistical evidence about the rate of potential exonerating causes.