Probability for the clinical encounter

Abstract

This chapter outlines three different interpretations of the concept of probability and explains why CauseHealth supports an understanding of probability as propensities, and how such understanding influences clinical decision making and medical investigations in general. For an illustration of the difference between the three perspectives presented here, imagine a situation in which we are going to cross a bridge with a heavy truck, and we want to evaluate the probability that the bridge will endure the weight of the truck. A frequentist approach would face this challenge by looking at how often similar bridges collapsed under the weight of similar trucks. A Bayesian approach would consider the information we have about the bridge and the truck, and would treat the probability as the value of how certain we are that an accident will (or will not) happen. The measure of such certainty will be updated every time we gain a new piece of information. The propensity approach would describe the probability using the qualities of the bridge, the truck, and the whole situation, and trying to understand the intrinsic disposition of the bridge to collapse under a certain weight. Such intrinsicality will be evaluated by investigating the properties at hand (height, length, solidity, material) and by understanding the causal and physical processes involved. All these perspectives - frequencies, uncertainty and propensities - offer something that can be useful for expanding our causal knowledge. The philosophical question is which we take to be basic.