Hypothesists were the third rank of the Mentat order beyond that of the Processor. They were trained to extrapolate from information to alternative explanations of the causes or the effects of that information.
Hypothesists often prided themselves on the number of differing interpretations they could see in a set of events. A sample question "How many motives might Muad Dib have had for walking into the desert?" might produce as many as seven possible reasons for his action. The Hypothesist would naturally provide his master with at least a two-place ranking of the likelihood of the interpretations he offered. The primary hypothesis was 92 to 98% reliable.
Commercially Hypothesists could be used to speculate on future market conditions commodity prices, outcomes of various economic tactics, and likely changes in consumption ot planets and populations.
Mentats of Hypothesist rank and higher, were barred from official Cheops competition; but enjoyed no special advantage at games of chance. E.g. if a roulette globe was imperfectly suspended, causing its operation to vary from strict randomness. Given a sufficiently large record of results of the globe, a Hypothesist could easily have ranked the likelihood of successive spins, but the assembling of the record would have required a lifetime spent at the gaming tables.