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Statistics Hacks by Bruce Frey

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Hack #34. Make Wise Medical Decisions

Medical tests provide diagnostic screening information that is often misunderstood by patients and, sometimes, even by doctors. Understanding the probability characteristics called "sensitivity" and "specificity" can provide a more accurate and (sometimes) reassuring picture.

As a consumer of medical information, you have to make decisions about behavior, treatment, seeking a second opinion, and so on. You likely rely on medical information—newspaper stories, your doctor's advice, test results—to make those decisions. However, much of the medical information you get from your doctor has a known amount of error. This is especially true about diagnostic test results that indicate the probability that you have a certain condition.

This hack is all about using information about the characteristics of those medical tests to get a more accurate picture of reality and, hopefully, make better decisions about treatment.

Statistics and Medical Screening

To use medical test information wisely, we have to learn just a bit about what the concept of accuracy means for these tests. The four possible outcomes of medical tests, in terms of accuracy, are shown in Table 3-11.

Table 3-11. Possible medical test outcomes

 Patient actually has the condition (A)Patient actually does not have condition (B)
Test result indicates patient has conditionTrue positive (score is correct)False positive (score is wrong)
Test result indicates patient does not have conditionFalse negative(score ...

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