We have described the adjustment of beliefs about a collection of quantities by observation of a further collection. Often, we will want to explore the ways in which different aspects of the data and the prior specification combine to give the final adjustment. (For example, we might be combining information of various different types collected in different places by different people at different times.) We now consider which aspects of the data are most crucial to the final adjustment, in order to produce efficient sampling frames and experimental designs, a priori, and to investigate diagnostically whether the various portions of the observed data have similar or contradictory effects on our beliefs.