5.11 Combining evidence
LRs can also be used to consider the combined value of multiple pieces of evidence together. This is useful when multiple pieces of evidence relate to the same pair of competing propositions. It is also useful for moving from the source level of proposition up to the activity level.
It is easier to see the connection between multiple pieces of evidence and competing propositions by using a graphical model. A graphical model is a visual representation of the evidence and case circumstances. Seeing the logical dependencies between the different pieces of evidence and the propositions allows us to clearly see the statistical dependencies that should be accounted for in the probability model for the evidence. This means that the probability and LR calculations can be made in the confidence that they accurately affect the case circumstances. This approach is becoming more popular amongst some scientific groups as more methodology is being developed. For example, Koeijer et al. (2020) present an approach that is useful for an interdisciplinary forensic examination at the Netherlands Forensic Institute.