FALSE POSITIVES OR FALSE NEGATIVES?
A speed camera is a compromise of all the factors described above, so it is impossible to make a camera that has pinpoint accuracy every time. The camera has to be made to a performance tolerance. Assume a speed camera is set to trigger at 32 mph. If a camera detects someone who is travelling at 31 mph and records them falsely at 33 mph, that is a FALSE POSITIVE. The motorist is recorded as positive when they were negative. If the camera fails to record someone when they were travelling at 34 mph, that is a FALSE NEGATIVE. The motorist was over the limit but the camera failed to detect them. False negatives and false positives are rarely an issue with our tests unless the urine or a control sample has a drug level very close to the cut off value, when the line will be faint. But the chances of a urine sample being very close to cut off at the time of test are remote. SUMMARY To summarise on cut off levels, rapid tests work just like a speed camera: The vast majority of the population w
