Calibration: A Frequency Justification for Personal Probability

If a physical theory states that the probability of some event, under certain conditions, is thus or so, we naturally take that to be a statement of objective fact, descriptive of the way the world is. And we expect that fact, if it is indeed the case, to be reflected in frequencies of occurrence among the described events. What is called the frequency interpretation of probability intends something more: namely, that such a probabilistic theory is reallyonlyabout actual frequencies of occurrence.1