In the second view, the probative value of the evidence (E) is not simply measured by the probability ratio, as is the case with the first view. Probative value is the extent to which E increases the likelihood that the sentence or hypothesis (H) supports (or against) that E leads. The certainty of E is measured by the difference between the probability from H to E given (the posterior probability) and the probability of H without E (the previous probability) (Friedman 1986; James 1941:699). It is important for an investigator to know that all aspects of their investigation can be disclosed as potential evidence for the court. As part of the fundamental justice process under the Canadian Charter of Rights and Freedoms, a person charged with a crime has the right to fully disclose all the evidence in the investigation (R. v. Stinchcombe, 1991). This means that any evidence or information gathered during the course of the police investigation must be available to the defence to examine and determine whether that evidence could assist the defendant in presenting a defence in court. Exculpatory evidence is any evidence that could exonerate the accused.

Defense teams often present exculpatory evidence to jurors to raise reasonable doubts or to justify or excuse an accused`s actions. The Brady Rule, first introduced in 1963, states that prosecutors are required by law to disclose any exculpatory evidence they find to jurors. The problem of the reference class is not limited to the probabilistic assessment of the probative value of individual evidence. This is a general difficulty in a mathematical approach to legal evidence. The same problem arises, in particular, in the case of a probabilistic interpretation of the standard of proof, where the court must determine, on the basis of all the evidence presented in the case, whether the standard is met. This topic is discussed in Section 3.2 below, but it is important to illustrate how the reference class problem can also occur in this context. This is because the plaintiff is suing Blue Bus Company for compensation for injuries sustained in an accident. The plaintiff testifies, and the court believes, based on his testimony, that he was hit by a bus driven recklessly. Unfortunately, it was dark at the time and he can`t tell if the bus belonged to the Blue Bus Company. Let`s further assume that there is also evidence that the Blue Bus Company owns 75% of the buses in the city where the accident occurred, and the remaining 25% belong to the Red Bus Company. No other evidence is presented. Using the data as a basis to conclude that there is a probability of 0.75 that the bus involved in the accident belonged to the Blue Bus Company appears to be the reference class of “buses circulating in the city” compared to other possible reference classes such as “bus travelling on the road on which the accident occurred” or “bus”, operating at the time in question” (Allen and Pardo, 2007a: 109).

Different reference classes can lead to very different probability ratios. It is crucial to know how the reference class is chosen, and it is ultimately a matter of reasoning and judgment. Any choice of reference class (with the exception of the class that shares each characteristic of the incident, i.e. the single incident itself) is in principle questionable. Simply put, traces are created when two objects come into contact with each other. Examples of traces of evidence include gunshot residue, hair, fiber, soil, wood, and pollen. Such evidence can help investigators associate an accused and/or victim with a common place. The conventional view is that relevance in law is a binary concept: evidence is relevant or not. As long as the probability ratio is not 1:1, the evidence is considered relevant. [9] However, the higher the 1:1 likelihood ratio, the higher the so-called probative value of the evidence (i.e., when interpreting the weight of evidence). We will take a closer look at the probative value of section 3.1 below. The term confirmatory evidence essentially refers to any type of evidence that tends to support the meaning, validity or veracity of any other evidence that has already been presented to the court.

Confirmatory evidence can take the form of a physical object, such as a DNA sample from an accused that matches the DNA found in a victim, thus confirming a victim`s testimony. Corroborating evidence may also come from the testimony of an independent witness who makes a statement consistent with the account of events described by another witness. If it can be proved that these two witnesses were separate and did not cooperate or listen to each other`s report, their statements could be accepted by the court as mutually confirmatory reports of the same event. A major difficulty with the two mathematical concepts of probative value we have just examined is that it is problematic for most proofs to obtain the numbers needed to calculate the probability ratio (Allen 1991:380). Exceptionally, there is quantitative data on the baseline level, as in our example of blood type. When objective data is not available, the investigator must rely on his or her experience and basic knowledge to find subjective values. In our blood type example, a critical factor in calculating the probability ratio was the percentage of the “suspicious population” that had the same blood type as the defendant. “Reference class” is the general statistical term for the role played by the suspect population in this analysis.

How to define the reference class of the “suspicious population”? Should we consider the population of the country as a whole, or the city or street where the alleged murder took place? What if it happened at an international airport where most of the locals are foreign visitors? Or what if it is proven that the accused and the victim were detained in the same prison at the time of the alleged murder? Should we then take the prison population as a reference class? The distribution of blood groups may vary depending on the selected reference class. Skeptics of mathematical modelling of probative value point out that data from different reference classes have different explanatory power and that the choice of reference class is open to contextual arguments and should be submitted and require the exercise of judgment; There is no a priori way to determine the correct reference class. (For the problem of the reference class in the legal determination, see Colyvan, Regan and Ferson 2001, in addition to the references cited in the rest of this section; Tillers, 2005; Allen and Roberts, 2007.) Demonstrative evidence can help illustrate or demonstrate a witness` testimony. It may contain a map of the crime scene or diagrams or images and images of the place that a witness describes. Conclusive evidence must accurately reflect the witness`s description. Various attempts have been made to find the answers (for investigations into these attempts, see Enoch and Fisher 2015: 565-571; Redmayne 2008, Ho 2008: 135-143, 168-170; Gardiner 2019b; Section 6 of the entry on legal probability). It has been argued that compliance with a legal standard of proof is not simply or fundamentally a matter of providing evidence to prove a mathematical probability of liability beyond a certain level. Standards of proof should be interpreted in epistemic rather than probabilistic terms. One interpretation is that evidence is sufficient to meet a standard of proof only if it is capable of justifying a total or total belief in the essential facts constituting legal liability, and mere statistical evidence, as in our examples, cannot justify such a belief. (Nelkin 2021; Schmidt 2018; Buchak 2014; Ho 2008: 89-99.) According to Smith`s account, the statistical evidence in our two examples does not justify believing in the assertion that the defendant is liable because the evidence does not support this assertion in a normative manner.

Evidence normatively supports a statement, just in the event that the situation in which the evidence is true and the sentence is false is less normal, in the sense that more explanations are needed than the situation in which both the evidence and the sentence are true. When all we have is statistical evidence, it could simply happen that the material statement is false (it could simply happen that the bus causing the accident is red or the accused is the one who refused to participate in the murder), so no other explanation is needed when the statement is false than there, where it is true (Smith 2018). To download a quick reference to the types of evidence described in this article, click Understanding Evidence Types. (a) a defendant may provide evidence of the relevant characteristic of the defendant and, if the evidence is admitted, the prosecutor may present evidence to refute it; Wigmore`s position on relevance is eerily at odds with his firm stance against the judge being bound to precedents in assessing the weight or credibility of evidence (Wigmore 1913).