## PV Curves for the Diagnosis of a Herniated Lumbar Disc After an Imaging Test.

The predictive value calculation for a test that can only be interpreted as positive or negative tells you the likelihood that the result, either positive or negative, is true and not false. With LOBAK you can find your pre-test probability (p) of a herniated lumbar disc (HNP). After an imaging study, their predictive values for each p-value have been plotted on the vertical-axis above. All imaging exams for HNP can have false-positive or false-negative results, roughly the same for myelogram, CT Scan or MRI.

For example, if your pre-test evaluation indicates only a 40% probability of having an HNP and your MRI scan shows no HNP, then your chance of having an HNP is reduced to 20% since (see graph) the PVneg is 80%. That’s well below the threshold for surgery, which is about 70%. But if your imaging test shows an HNP, then your chance of having one is about 80%, as PVpos is 80%, and that is above the threshold for surgery.