David Poole wrote: > > (2) "Often" and "credible" are imprecise descriptions of something > > probabilistic.Bayesians typically insist upon precise numerical > probability. Some > > others relax that, but still require numbers which, say, bound probability > > intervals. > >Bayesians are like that because we have to make decisions. I'm quite >happy to have abstract problems (like the one Lotfi Zadeh posed, for >which the answer is "probability that Robert wears large-size shoes is >bigger than 0.5") but when I have to act, I have to decide on something. >If my decision doesn't depend on which value bigger than 0.5 is the >appropriate value, then I could pick any value and make the same >decisions. If my decision does depend on which value, then having the >range doesn't help. When I make a decison, I am implicitly assuming a >particular value. So I might as well have the value that best reflects >my knowledge.
A major focus of UAI seems to be building computer systems that assist us in taking decisions. I am happy with systems that can recognize the limits of their knowledge and suspend the judgment when these limits are reached, in the same way that I prefer to be told "I do not know" when I ask for road information rather than being recommended a wrong route. Also good human experts know when they should suspend the judgment. Having to occasionally suspend the judgment is logical consequence of working with probability intervals, or with more general frameworks (e.g., lower probabilities and previsions). So intervals are likely to be needed by real rather than abstract problems. What about having to make a decision? Consider a prospective expert system to diagnose a disease, which, given information on a specific patient, tells the doctor: given my current knowledge, I cannot decide between "disease" and "no disease". This is likely to motivate the doctor to look for further sources of information externally to the system, for example, by examining recent medical literature, by asking more experienced colleagues, by doing medical tests that are not considered by the system, etc..., in the direction of reliable diagnosis. This appears to be a safer approach to reduce the uncertainty than making strong assumptions to have the expert system always produce determinate conclusions, perhaps making it produce "no disease" in some occasions when the evidence does not actually justify this. Marco ----------------------------------------- Dr. Marco Zaffalon Senior Researcher IDSIA Galleria 2 CH-6928 Manno (Lugano) Switzerland phone +41 91 610 8665 fax +41 91 610 8661 email mailto:[EMAIL PROTECTED] web http://www.idsia.ch/~zaffalon -----------------------------------------
