A false positive rate of close to 50% means that every second alert indeed pointed at something real. That should not cause the staff to get unmotivated. Again, without the false negative rate we can't judge if they are complete bullshit or not. If it were a 90% false positive rate then sure, that would clearly have the effects you outlined. I don't think at around 50% that's the case yet.
> The false positive rate is calculated as the ratio between the number of negative events wrongly categorized as positive (false positives) and the total number of actual negative events (regardless of classification).
No, it means that about 50% of people scanned would trigger a "positive". The false positive rate is the number of false positives divided by the number of actual negatives.
100 people, 50 false alarms, 1 actual problem alerted and 49 marked as safe correctly = 50/(50+49) = ~50%.
Wow, that definition is counter-intuitive. Ive expected the false-positive-rate to be the number of false positives divided by the number of all positives. Isn't it how "rates" are usually defined? No wonder everybody is confused.
I think it's a perspective thing. You are looking at the rate of false results, so given a particular type of input what rate do you get it right? For negative ground truth your possible outputs are "false (positive)" and "true (negative)".
I agree it can be confusing, but I think people would also make the opposite mistake if it were defined differently.
False positive = (Machine says positive but grand truth is negative) / (Machine says is positive)
In English, a false positive is when the machine declares something as positive but it is actually negative.
This fits a sanity test because ~50% of people that pass through a detector do not get patted down. The truth is closer to 10%. Even then, a true positive probably includes someone with two pennies in their pocket.
You are right this is ML 101, but you are wrong. Someone else has linked the wiki page, and I've posted it elsewhere and I would strongly recommend you read it as your interpretation is very incorrect.
> In English, a false positive is when the machine declares something as positive but it is actually negative.
Yes, and the rate is based on the frequency this happens in your negative set.
>This fits a sanity test because ~50% of people that pass through a detector do not get patted down.
The 50% figure may be wrong, but my definition of what a false positive rate is not.
Please see my other comment which references the definition of false positive rate because I think your understanding of the term is wrong. You have a 50% alarm/trigger rate in mind. And please try to reply with a bit more substance than "No".
To quote an article on the subject: "meaning that every other person who went through the scanner had to undergo at least a limited pat-down that found nothing"
> And please try to reply with a bit more substance than "No".
Eh. I was hoping you'd just delete the comment rather than have two parallel arguments.
