Edit: "accurate as a coin flip" is a bad construction, but I wouldn't exactly expect better from a newspaper. The information gain from a device that activates randomly 50% of the time, 0% of the time, and 100% of the time are all the same, which is to say zero.
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93% alert rate means:
93% = false positive + true positive
7% = true negative + false negative
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We're given "His success rate was much lower, at 59 percent." Assuming that means that 59% are true positives, we know the false positive rate is 34%.
Without data on how many passengers are carrying drugs, we can't say anything about the rest of that result. A plausible world where the drug dog may be valuable is when he unquestionably rules out that 7% of the population that he doesn't alert on, as in false negative = 0.
I believe the reason this number is so high (59%) is that the officer has already used his suspicion to determine filter out most people. This makes the value of the "ruling out" plausibility even more valuable: the drug dog reduces searches compared to trusting the cop.
Ideally, they'd provide the receiver operating characteristics curve [0] or the confusion matrix [1].
[0] https://en.wikipedia.org/wiki/Receiver_operating_characteris... [1] https://en.wikipedia.org/wiki/Confusion_matrix
I say this because it is possible (and indeed likely) that the officer is also better at guessing who has drugs than a coin toss.
Full Disclosure: I have never used or trafficked contraband, but I do not support random searches or the use of drug dogs in public without a warrant, regardless of their effectiveness.
A very big problem is that drug dogs will alert when the handler gives it subtle clues. This is done to get probable cause for a search when there is nothing more than an officer's hunch or just a desire to hassle a particular individual.
The primary trouble I see is that there is no penalty for re-training dogs like this.
>This is done to get probable cause for a search when there is nothing more than an officer's hunch or just a desire to hassle a particular individual.
that claims that this is done purposefully. That's what I was wondering about, not the overall efficacy of drug dogs.
https://youtu.be/w-WMn_zHCVo?t=3m35s
It happens.
http://www.ucdmc.ucdavis.edu/welcome/features/2010-2011/02/2...
There are many examples that have been caught on camera, I see that another commenter posted a link to one of them on this thread.
When you see things like the handler returning to a previously cleared spot and indicating that the dog should check it again; three or four times until the dog alerts, you can assume that the handler has a severe short term memory problem and he just forgot that the dog had previously checked the area and failed to alert. I think it's more indicative of the officer hinting to the dog that "this is where I want you to alert" and their training reinforces the idea that if the dog does what's expected, there will be a treat.
My last dog picked up on so many of my personality traits/tells-- I felt quilty.
(My cat--whole nother story.)
Even more so, I think that is actually what is happening here. An officer is acting as a tier 1 filter, and then the drug dog is acting as a tier 2 filter, further reducing the number of false positives, which in a "legal and ethical" sense, we generally feel are worse than false negatives.
If the officer is acting as a filter, then it seems to me like this is a search, and not allowable, because it would be subject to all the usual objections to random searches. You might be right, but if that is the only way for these searches to be better than the officer's guesses, it seems that drug dogs would not be allowed to 'sniff' in public without warrants.
More worryingly, that also means that out of every hundred cars stopped, 38 are wastefully searched by police (after getting probable cause from the positive dog alert) without finding drugs. From the article, a search takes about 45 minutes and carries a bunch of other risks for occupants of suspected cars (e.g. civil forfeiture, overenthusiastically trigger-happy LEOs), so this is pretty bad situation, not just in wasted time and cost, for both the car occupants and the police force.
One slightly positive thing I'll take from this: Over 50% of cars that are dogged have drugs, and I sincerely doubt that over 50% of cars (on average) have drugs, so in this particular study it appears that police have a better than random chance of guessing which cars have drugs. It's not a very positive thing though, because civilized countries that operate under the rule of law cannot permit law enforcement to operate on guesswork. This is underlined by the fact that the article mentions that the false positive rate rose to something like 80% for latino drivers.
I agree with you mostly - especially on the discussion of what "probable cause" should be defined as and what constitutes a "random" search, as just an example of some of the ethical issues of interest here. That is a debate to have and even one I think this community is well equipped to discuss, but it was not something I was trying to comment on.
I was only making the point that it wasn't fair to jump on the 93% as though it was representative of the problem. I am not taking any ethical or defensive position of drug dogs here.
I found it impressive that the dog that alerts 93% of the time was correct 40% of the time. That means the police are doing what seems like a good job of identifying targets that actually have drugs. With those kind of odds, you'd probably want to take a closer look at everyone just to make sure you aren't letting people with drugs get away (false negatives).
Then for 1000 stopped, you'll have
0.59 * 0.1 * 1000 = 59 true positives and ...
0.34 * 0.9 * 1000 = 306 false positives.
That's pretty terrible.
The article indicates that of all the people the dog indicated had drugs 59% of them actually did. So for 1000 people whom drug dogs are called on
930 the dog indicated had drugs. Of those 549 were correct and 381 were false positives.
I'd compare it to the fact that lots of very hard certification tests actually have fairly high pass-rates (80% or above), simply because people who don't think they could pass don't take the test to begin with - The 80% pass-rate is not representative of the average person's chances of passing the test, nor the difficulty of the test itself.
What's really important is the percentage of those positives which were true positives, vs. false positives. In this case, you would expect the number of positives to be high - The number of true positives vs. false positives would tell you how accurate the dog actually was in the positive case. If this number is also high, then the dog is doing a reasonable job. Of course, to derive a real argument from this, you'd need to know the number of true and false negatives as well, but obviously we don't have that information.
In other words: If we wanted a drug dog to be as close as possible to a coin flip, we'd just flip a coin instead.
Imagine if it was bombs they were sniffing for. We'd be happy if they found even one more bomb.
Why even bother with the dog? why not just do random searches? Oh wait, because that would be unconstitutional. The dog exists solely to justify otherwise unconstitutional searches.
Or maybe just 93%.
At that point you might as well give up on faffing about with a sniffer dog and just search the remaining 7%.