 There are some further subtle differences between the two results. First, Olsson’s theorem is proved against the backdrop of a dynamic (or, in the language of Bovens and Hartmann, 2003, endogenous) model of reliability: the assessment of witness reliability, which in this model is represented as a probability of reliability, may change as we obtain more reports. Bovens and Hartmann’s detailed proof assumes a non-dynamic (exogenous) model of reliability, although they indicate that the result carries over to the dynamic (endogenous) case. Second, there is a difference in the way the ceteris paribus condition is understood. Olsson fixes the initial probability of reliability, but allows the prior probability of the report contents to vary. Bovens and Hartmann fix not only the reliability but also the prior probability of the report contents.