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PSA Standardization



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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