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Effect of Analytical Bias on Classification Based on Fixed Criteria

Slide 17

October 2009

If we simply examine the effect of analytical bias alone on classification that is based on a fixed criteria, it may be more obvious what this means. Let’s say these curves represent a distribution of patients who have their PSA measured. On the right side of the curve we have our fixed decision threshold (in this case we’ll use 4.0 ng/mL) and the marked area represents our patients with a disease (prostate cancer) we want to detect.  If we have an analytical shift in the calibration then we move the curve to the left by 20%.  If the cutoff does not shift to match the lower patient results, then the number of patients we detect simply decreases. This, in a very simplistic explanation, is what we see between Hybritech and WHO assays if the cutoff does not change.

Analytical Bias

 


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