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MIT's January 2004 Technology Review selected Bayesian systems as one of the "10 emerging techologies that will change the world." Bayesian belief systems can be created from raw data, without prior assumptions. They "learn" from the initial data and then continue to learn from each new data entry. Bayesian systems can also be created by experts, who create the initial assumptions, and then refined by ongoing data. They thus transcend the limitations of evidence based medicine and of expert opinion. A simple example will illustrate their power. The belief system for a car (see figure), designed to evaluate one that will not start, is illustrated in the diagram. The belief system contain nodes that can be evaluated. Nodes are linked together based on the assumptions of the belief system. A cost can be attributed to testing each node. As a test of the battery, it would be less expensive to turn on the lights rather than replacing the battery. Once constructed, this sytem can ask you questions. If you start with only an understanding that engine will not start, it asks whether the engine turns over. If it does not, then it asks whether the lights turn on. If it does turn over, it will ask for a reading from the gas gauge. With each response it will give the probability for each node as the potential source of the problem. Thus, before you replace the starter, you will have a high probability that it is the problem. The Bayesian belief system provides some interesting insights. These are often not obvious from the raw data (the battery is essential for starting), but are intuitively clear upon reflection. The battery is not directly linked to the engine starting in the illustration and our conclusions about it can be quite accurate with looking directly at it. | ![]() | |
| Similar belief systems can be created for a medical issues, such as weakness. Creating such a system changes ones perspective on the problem and focusses attention on the problem solving aspects of the task being pursued. Traditionally physicians look at the spinal cord, anterior motor neuron, nerve and neuromuscular junction as a continuous pathway directly connected to the muscle. In the Bayesian modeling, the deep tension reflexes emerge as an early question. This is intuitive to the experienced clinician, but clearly evident to everyone with this construct. In this example the Bayesian belief system was populated by estimates of the relative probabilities by an expert. It could be populated by actual data from a set of patient's clinical records. Once these probabilities are available, predictions can be made. However, further information would help prioritize the questioning. Some things are easy or low cost; others are painful or expensive. With a fully informed Bayesian belief system, these factors would be considered and the least expensive, risky or painful course selected. These selections would perhaps suprise a clinician, but they would be intuitive upon reflection. The next few items illustrate how observations alter probabilities. |
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| The initial probabilities, given only weakness indicate the relative frequency of diagnoses of muscle, nerve, anterior motor neuron (AMN), and spinal cord. | ![]() | |
| Given the lack of reflexes, the probabilities (in a child) shift strongly to the anterior motor neuron. | ![]() | |
| A distal sensory loss changes everything and makes the nerve the most likely localization. | ![]() | |
| An excellent study from Intermountain Healthcare is also instructive. Lagor, et al. trained and tested a Bayesian network and an artififical neural network from data on 32,662 adults with presumptive community acquired pneumonia (CAP). Both networks had excellent accuracy in predicting qualification for the CAP treatment guideline. They utilized Netica software for their research. | ![]() | |