11.1 NHST for the Bias of a Coin 267 Notice that for any of those intended experiments (fixed N, fixed time, or fixed z), the actually observed data are the same: z = 8 and N = 26. But the probability of the observed data is different relative to each experiment space. The space of possibilities is determined by what the experimenter had in mind while flipping the coin. Do the observed data depend on what the experimenter had in mind? We certainly hope not! A good experiment is founded on the principle that the data are insulated from the experimenter's intentions. The coin "knows" only that it was flipped 26 times, regardless of what the experimenter had in mind while doing the flipping. Therefore our conclusion about the coin should not depend on what the experimenter had in mind while flipping it. This chapter explains some of the gory details of NHST, to bring mathematical rigor to the preceding comments and to bring rigor mortis to NHST. You'll see how NHST is committed to the notion that the covert intentions of the experimenter are crucial to interpreting the data, even though the data are not supposed to be influenced by the covert intentions of the experimenter.