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When a patient sits
down in your office and says, "Doctor, I have chest pain,"
you begin a game of guessing what is going on under that person's
skin. Since you can't be certain without doing something implausible
like examining a potentially diseased organ with your naked eye,
you must make a choice without being sure it is the right one.
Information can help
you reduce your uncertainty. Probability theory is the language
of uncertainty. It allows you to reduce your uncertainty about
how uncertain you are about the cause of the patient's symptom!
When asked how sure
they are of their diagnoses, most physicians express their degree
of certainty in words. An alternative to using words is to use
a number -- namely, the probability that the diagnosis is present.
| Definition
of Probability
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| A
probability is a number between 0 and 1 expressing
the likehood that an event will occur.
- 0
represents certainty that it will not occur
- 1
represents certainty that it will occur
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In the case study that
follows, you will see how probability can help reduce uncertainty
in the medical decision making process.
Odds and probability
are two equivalent ways to express uncertainty. This chapter
moves back and forth between them often.
If you don't understand
the relationship between the odds of disease and the probability
of disease, click on the FYI box below.
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