Probability of False Indication and Probability of False Positive 

PFI/PFPProbability of False Indication and Probability of False Positive are measures of the likelihood of an NDT technique resulting in the sentencing of a signal as being from a defect when there is no defect present. The defect detection capability of an NDT technique is often expressed by probability of detection (POD) (see ‘What the Hec?!’, June 2006). The POD of a technique can often be increased by lowering the detection threshold, ie increasing the reporting sensitivity. However, this can lead to noise signals breaking the threshold and being reported as defect indications, which can potentially cause as many problems as missing a defect.

An optimum technique is one that provides the required POD with an acceptably small PFI/PFP.

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