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“There are three kinds of lies: lies, damned lies, and statistics.”
I am certain many readers will be tempted to shy away from reading about how the mathematics of lab testing works, but if you stick with it, Dr. Susan Leclair’s two articles that follow will give you the opportunity to gain helpful insights, not only into understanding your own CLL test results, but also to acquire a good grasp of the current data about COVID-19 results and any other testing data.
Her first article, MRD Part I Counting Marbles: The Hunt for Residual Disease, deals with the increasing sensitivity or ability of the available tests to detect very small amounts of (minimal) residual diease (MRD).
The second article, MRD Part II Test Attributes: Sensitivity & Specificity Matters, delves into the definitions of sensitivity and specificity and shows, when dealing with a condition that has a low prevalence in the group being tested, the sometimes surprising but mathematically powerful implications of even low false negative and false positive rates.
For example, if the disease is found in only 1 in every 300 people, and the test had a false positive rate of 1%, if you tested 3,000 people, there would be 10 true positives and 30 false positives. The odds of your positive test being a true positive would only be one in four.
Well worth a read!
Originally published in The CLL Society Tribune MRD Special Edition.