Stop and Search

[Profpointy]

ooh, get you

anyhow to backtrack slighlty the picture did deserve a titter to be fair

 

[Joey Shabadoo]

"searching all" - seriously?

In reality, no, of course not but if the perception amongst the target group is that they will in all likelihood be stopped then those that can be deterred will be.

 

[swansonj]

I hope that you and @Profpointy will forgive me if I don't provide you with a full worked-through proof, or a reference. I may well have read it in a Goldacre book; if not it could be in any one of a couple of dozen books that apply statistics to understanding the world.

By focussing on [group X] for your stop and search you are essentially asserting that P([bad thing] | [group X]) is enough higher than P ([bad thing]) that you will make a significant difference. In fact what you know is that P([group X] | [bad thing]) is higher than P([bad thing]), which isn't the same thing. Once you take into account the negative impact of focussing on [group X] you end up doing more harm than good.

The argument (which I've probably misrepresented) is very similar to the argument that X-ray screening might not be an effective tool for breast cancer detection, or that [expensive drug Y] isn't actually a good choice of treatment for [disease Z], or indeed that helmets aren't an effective intervention for increasing cycle safety.

Feel free to make my argument more robust....

I think you're saying that if the rate of, say, knife crime, is low, say 1%, then even even if it's ten times higher among Shell Suit Wearers, then 90% of stop and searches among SSWs are still going to be negative, not an awful lot better than the 99% if you don't do any targeting. So that's a valid argument against the principle of stop and search: stop and search aimed at whole communities ain't ever going to be much good at detecting rare crimes. On the other hand, if you decide for external reasons to do stop and search, and you have a notional quota, you are still better off targeting that quota on SSWs?

On the other hand you might be saying something altogether different my brain is a bit tired tonight

(Are conditional probabilities really Bayesian? I'm sure I'd learnt them before I ever heard of Bayes and his theorem...)

 

[Profpointy]

In reality, no, of course not but if the perception amongst the target group is that they will in all likelihood be stopped then those that can be deterred will be.

swanson's elaboration of the argument just below your post puts very clearly why that maybe a bad idea. Basically you get nearly as many false positives amongs the "bad" group as the "respectable" group even if the former are 10 times as "bad".

I was thinking on similar lines, but couldn't quite remember the logic

 

[Tim Hall]

Presumably the relative sizes of the "good" and "bad" groups will play a part in this, as will the fact that the number of stop and searches that can be done is finite, limited by manpower and/or time available.

 

[Flying_Monkey]

[QUOTE 4517751, member: 76"]It's got all very SC&P in this thread hasn't it?[/QUOTE]

I'm not quite sure why this thread wasn't in SC&P to begin with or why some people insist on starting obviously political threads in the café and then being surprised when they get, err, political. And it seems to me that these café politics threads are actually often turn bad-tempered and less well-argued more quickly as a result of this lack of comprehension.

 

[slowmotion]

The last time I was searched was thirty years ago. I was walking back from the local offie, down a quiet residential street close to my home, with cans of yellow beer in a carrier bag. A police car screamed to a halt and I was asked to show the contents of my swag bag. I asked them why I had been stopped....

"You crossed the road suddenly, Sir"

 

[lutonloony]

I'm still confused by the map, let alone all the statistic malarkey

 

[classic33]

I'm still confused by the map, let alone all the statistic malarkey

Local force have a high rate, but the map doesn't show that.

 

[Brandane]

And it seems to me that these café politics threads are actually often turn bad-tempered and less well-argued more quickly as a result of this lack of comprehension.

Ooh; get you!

 

[slowmotion]

Ooh; get you!

I think he went to college.

 

[MarquisMatsugae]

The last time I was searched was thirty years ago. I was walking back from the local offie, down a quiet residential street close to my home, with cans of yellow beer in a carrier bag. A police car screamed to a halt and I was asked to show the contents of my swag bag. I asked them why I had been stopped....

"You crossed the road suddenly, Sir"

Maybe a very drunk man had recently reported his cans of beer missing.


(Getting coat on)

 

[threebikesmcginty]

I agree this should be in P 'n' L, I wouldn't suggest that anyone not posting within the context of the debate is thick though, some folks post in the cafe for a bit of fun* and have also been to polytechnic and have a proper job where they have to think and stuff.

*this doesn't mean casual racism and sexism so leave it.

 

[threebikesmcginty]

The problem with moving some threads from cafe to SC&P is that some self-exiled people then spit the dummy.

Feck em.

 

[Brandane]

The problem with moving some threads from cafe to SC&P is that some self-exiled people then spit the dummy.

Ooh get you too; I don't know who you could possibly mean!
I did it because I was the starter of that particular thread and didn't see why my effort should then go over to the dark side for their entertainment.
As was discussed at the time, some political subjects can be of interest in the café too, but we prefer to discuss them in a more light-hearted way.