 We will not presuppose any particular interpretation of probability (see the entry on  interpretations of probability),  but we will assume that frequencies in appropriately chosen samples provide evidence about the underlying probabilities. For instance, suppose there is a causal model including the variables E and I described above, with \(\Pr(E = 3) = .25\). Then we expect that if we survey a large, randomly chosen sample of American adults, we will find that approximately a quarter of them have a Bachelor’s degree, but no higher degree. If the survey produces a sample frequency that substantially differs from this, we have evidence that the model is inaccurate.