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Archive for April 2nd, 2008

How Examinations And Diagnostic Tests Are Similar

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“You are more than a score”, or so the saying goes. But how much of that comes out as an emotional outburst as opposed to objective and rational thinking? Let’s try to see why the above is totally true, scientifically speaking.

In medicine, we’ve learned a lot about diagnostic tests, right? In fact everything investigative in nature can be considered a diagnostic test. Be it a screening exam for cervical cancer, that blood test for glucose, an X-ray for a broken arm, or your palpating hand feeling for that enlarged liver. Heck, even an entire research study could be considered a diagnostic test. The ‘null hypothesis’ technique often used in analytical research studies is nothing more than a diagnostic test of sorts.

When considering the dynamics of a diagnostic test, a fundamental underlying principle is that we separate what is observed via the test from the actual truth. In the case of tangible phenomena like death, disease and disability, it is quite easy to distinguish the actual truth from what the test predicts. Because of this, you have terms like ‘false positives’, ‘false negatives’ and the like. A pregnancy test for example could be positive, but you could easily compare that prediction to the actual outcome (pregnancy vs. non-pregnancy) and say that this particular test has got such and such false positive rates. More or less, all tests have the following attributes in this regard:-

  1. Sensitivity
  2. Specificity
  3. Positive Predictive Value
  4. Negative Predictive Value
  5. Validity/Accuracy
  6. Reliability/Precision

We ought to think about examinations such as the USMLE, etc. in this manner as well. Why? Well, because they are investigations too! Think of them as X-rays to diagnose your intelligence or whatever, if that metaphor helps. And as a consequence, notions about false positives, false negatives and all of the other things on that list also apply to them. Being the abstract intangible thing intelligence is, it is impossible to know its true value. And because there’s no way to compare prediction versus truth, it is impossible to say for sure what the false positive or negative rates (or any item on that list) for an exam are. And that’s why, ‘you are more than a score’ ! Statistically speaking, examinations are just so lame !

Do send in your comments!

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