Abstract

In deciding whether an event was caused by chance or agency, it is incorrect to attribute the event to chance on the grounds that there have been enough broadly similar situations in the universe to provide opportunities for the event to occur by chance somewhere or other. In order to include a set of instances in an inference as opportunities for the event to occur by chance, we must calculate the impact of the other proposed opportunities upon the prior probabilities of chance and design and argue that the absence of a result confirming design in the other instances directly drives down the prior for design in the instance at hand. This approach forces us to narrow our focus to those instances which are directly relevant to a causal inference about the case at issue, and it avoids confusions generated by treating all broadly similar instances as a lottery that is nearly guaranteed to have a winner if the set is large enough.