Within the frequency probability framework, there is no process whereby a probability can be attached to the future occurrence of special cause. One might naively ask whether the Bayesian approach does allow such a probability to be specified. The existence of special-cause variation led Keynes and Deming to an interest in Bayesian probability, but no formal synthesis emerged from their work. Most statisticians of the Shewhart-Deming school take the view that special causes are not embedded in either experience or in current thinking (that's why they come as a surprise; their prior probability has been neglected—in effect, assigned the value zero) so that any subjective probability is doomed to be hopelessly badly calibrated in practice.