Keeping a weather eye on the crime stats
Does rain explain the latest jump in recorded robberies at knifepoint?
The official statistics show an 18% rise in such offences in England and Wales - widely reported as evidence of the "epidemic" in knife crime.
But could the increase have more to do with the weather?
I know what you are thinking: it's Easton on one of his hobby-horses. But bear with me.
The first thing to say is that looking at raw numbers, there were roughly 700 more robberies conducted with knives in July to September last year compared with the same period in 2007.
But overall robbery was down by 500, so there must have been 1,200 fewer robberies of other kinds - those involving firearms, baseball bats or the threat of physical attack.
That strikes me as worth mentioning - after all, being robbed at gunpoint is probably just as traumatic as facing a blade.
The 18% reflects the difference in knife robberies in the late summer of 2008 compared with 2007. But what if we look at the months around those two quarters?
The Home Office has kindly sent me figures and they show that in each 90-day period from April 2007, there were roughly 4,000 to 4,300 robberies involving a knife or sharp instrument. A pretty flat picture - except for one quarter.
In July to September 2007 there were just 3,500, an unusually low figure that one might attribute to one of the wettest summers on record.
People didn't fight each other so much, perhaps, because they were staying out of the rain. I can't be sure, but it could be that the big jump has less to do with criminology and more to do with meteorology.
I'm 
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I have just posted comment in your item more statistical fury [2]
- The statistics office having to be fair and accountable to a watchdog UK Statistics Authority - an authority pledged to rebuild confidence in government data- looking to make an example of some one.
To which I commented - so no bias there then. - A comment which is born out by your observations that the latest crime figures from the home office have more to do with the weather than our political leaders policy so here is the rest of my thoughts on statistics and this government. I believe more suitably positioned here.
Should they not be trying to rebuild accuracy and provide the customer [the British electorate] with the correct data not make Gordy and the crew look good?
Why cant government and all civil servants remember to whom they are supposed to be civil and whom they serve
How is anyone going to moderate a department whose very performance will always come up with the result that - a man with his head in the fridge and his feet in the oven is on average comfortable - other than by bias?
The entire shower in Westminster should be washed down the gutter it has created for us all [the public] to live in and the electorate be allowed to choose some representatives who can get us on the move again with accurate accounting
There is little I would look to America to provide example or inspiration in but there is one thing why don’t we insist the we stop calling politicians – politicians – and call them representatives that might remind them every day when they get out of bed what they are suppose to be doing - that is looking after the best interest of the people they represent - instead of feathering their own nest and trying to protect their own butt while attempting to lick that of their colleagues higher up the ladder.
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Mark Easton's probably right. Criminals are generally lazy so rain is a mitigating factor.
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Your theory seems to have a lot more going for it than the spin the government tried to put on the figures. But then your suggestion is rooted in the logic of the real world. Politicians seem to live in a world where a whole other kind of logic, only meaningful to other political animals, holds sway. Thank goodness for journalists who try to poke holes in the Emporers' clothes!
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You could also attribute the fewer number of knife-point robberies to the longer daylight hours in the summer months. Rain is hardly a mitigating factor, whereas a robbery is far more likely to take place in the dark or dusk.
Sounds to me like your link between rainfall and knife crime was just a wild stab in the dark.
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All the anecdotal evidence I have heard points to the police being less busy during rainy weather and that heat waves lead to increased violence.
It makes sense to think that people are less likely to be hanging around outside a pub looking for a fight when it's raining. The same would hold true for robberies - less people in the streets means less robberies. It would be interesting to see if burglaries increased in the same period - muggers trying to keep dry?
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According to the met office (http://www.metoffice.gov.uk/climate/uk/2007/rainfall.html) 2008 had a higher rainfall than 2007 in both Aug and Sep. It was only July that was wetter in 2007.
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Yes, I`ll agree with this theory. On the continent in the 60`s they used water cannons to clear rioters from the streets.
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In order to see whether the drop in robberies for July-September 2007 is weather-related, it would help to see figures for periods going back around 10 years. In particular, I would be intrigued to see whether Summer 2003 saw a rise in robberies.
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"boisterousblahah wrote:
You could also attribute the fewer number of knife-point robberies to the longer daylight hours in the summer months. Rain is hardly a mitigating factor, whereas a robbery is far more likely to take place in the dark or dusk."
The point is comparing the same month with the previous year, i.e. July 2008 to July 2007.
The daylight is the same each year, but in a wet year (like 2007) people stay indoors and don't commit robberies, giving a low base figure.
It's like saying my fish & chip consumption doubled from August 2007 to August 2008, neglecting to mention that in August 2007 I had a 2 week chip-free holiday out of the UK.
You need to compare like with like, not just look at plain % rises.
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Mark's theory makes sense to me. When riots erupted all round the country in 1981 there were political triggers, but those same potential trigger events happen month in month out without similar reaction. I said at the time, and I still believe, the main trigger wasn't anything political, it was the weather: hot hot hot.
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This seems to me to be a classic case of the "correlation does not imply causation" logical fallacy.
There has been an increase in the production of greenhouse gases in the last 200 years in tandem with a decrease in the number of pirates (a la blackbeard), therefore pirates protect against global warming! (see 'church of the flying spaghetti monster' for details). This may seem more ridiculous than "rain reduces knife crime" but the idea is the same - simple comparison of independent events rather than consideration of actual causes leading to false conclusions.
Until proper evidence based research is done to back up such correlations - Beware the logical fallacy! - it lurks around every corner waiting to stab with the knife of misinformation and pilfer the wallet of common sense!
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Firstly I think people need to be very cautious about figures that originate from the police - anyone who has dealt with them will be able to tell their own little story/s of how the police hide crimes.
Rain and reduction in street robbery? Not unreasonable. As other people have noted the same phenomenon happens with riots in some communities. In hot weather some people hand around on the streets and any provocation can rapidly spread from one group to another. If they are all inside, sheltering from the rain then it doesn't spread.
I have heard experienced police officers refering to 'sergeant rain' in the context of publice order. They look at a surly group of protesters etc and state, 'here comes reinforcements, sargeant rain will soon settle them' - at the very least it dampens their mood, at best they all just go home.
Not unreasonable to suggest a similar phenomenon with street robbery.
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But physics_bloke ... maybe I should've called myself maths_girl to increase my credibility? ;o) ... Mark's suggestion _is_ a common sense interpretation of the stats. I walk my dog in all weathers, but the number of other dog walkers I see on cold wet days is far less than on balmy sunny ones ... a little life experience teaches us that most people don't much like going out in the wet. Why shouldn't that apply to criminals too? They're still people, just not very nice ones. It is perfectly reasonable to suggest they would rather stay indoors when it's chucking it down. Obviously it's not a proven cause and effect, but it's a good contender for an explanation.
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Coincidence is not correlation
Correlation is not causation
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#13
It may well seem to make sense with personal experience, but then so did house prices always go up, for anyone who looked at house prices between say 1997 and 2006. It doesn't make it true however.
Experience has also taught me that most people look for evidence that supports their own pre-formed conclusions. And we know that Mark is firmly of the view that violent crime is falling, hence looking for an explanation that can support his view in the face of evidence to the contrary, should not be surprising.
To be honest I don't know what we can take from the statistics - the methodology changes almost every minute, so we can never truly compare like with like. Of course, not being able to truly compare would be a good way of "burying bad news", to put some spin into the equation.
And the one thing that we can truly be sure of, is that politicians (and this government in particular) do love to spin.
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I may be missing something here but, if the wet weather in summer 2007 was a factor in the increase in robberies at knifepoint for the same period in 2008, why didn't it affect other robberies in the same way?
Mark says that overall robbery declined by 500 over the period. Surely the inference then is that that baseball bat and gun-wielding robbers are somehow less susceptible to rain and are built of sterner stuff than the average knife attacker?
Or am I just being thick?
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May be it is worth repeating the point I made in #6. For the period in question it rained more in 2008 than it did in 2007.
This isn't a case of confusing correlation with causation. It is a case of not checking all the data.
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I dont think weather affects crime.
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Sorry Mark but why should rainy weather affect the overall level of crime?
A bad weather day might simply mean that some criminals stay at home in bad weather and do more crime when the weather improves.
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"This seems to me to be a classic case of the "correlation does not imply causation" logical fallacy".
Possibly true, but causation always means correlation: i.e. if there is a cause there would be a correlation.. it's the first peice of evidence. It's a small sample, sure, but Mark has found a correlation and hypothesised the cause. It seems plausable; I don't go out as much in the rain and neither do people I know, hence we stand less chance of being mugged in the rain than in the dry (simply due to the base rate). I'd be surprised if the same is not true of most people.
I totally agree that one would need research to give sound supporting evidence, but it's an interesting idea, and I don't think it's so flawed simply because it's just correlation... there appears to be at least a little evidence FOR causality (i.e. the correlation) and none against.. yet.
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18. At 1:04pm on 23 Jan 2009, SheffGilly wrote:
I dont think weather affects crime.
It does - especially when you're talking about crimes of opportunity that are committed outdoors. If there are fewer people outdoors, then there are fewer people to commit crimes against.
Surely though, the real point is that the government are making comparisons with 2007 levels and claiming that there's been a huge rise. In reality, it's the 2007 figure that is the anomalous result by being unusually low.
Can we report them to the Advertising Standards Authority?
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MonkeyBot5000 wrote that weather affects crimes "especially when you're talking about crimes of opportunity that are committed outdoors. If there are fewer people outdoors, then there are fewer people to commit crimes against".
Quite. But that is not to say that when the weather improves that criminals don't make up for lost time and commit more crimes to make up for lost time!
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Ever considered that its darker over this period of time and that its seasonal rather than anything else.
If your going to rob someone at knife point would not the evening/night/earlymorning be better. is there a statistic for the time of day each crime is commited or just that they happened ?
I know if i was going to do such a crime i would want as much cover as possable and shadows to slip into afterwards.
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hmm that last comment was backwards ignore it :)
what i was actually thinking was how many of these crimes occur outdoors and at what times are they? evening morning or at night, did the crime happen during before or after the rain?.
but as i said at the end of the last comment i would choose night raining and opportunity to aid in not being caught as the other times leave you open to more risk of identification.
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Police crime stats at best reflect trends rather than actual crime figures. They are crimes reported to the police, so you may suffer a an injury and even get youself to A&E and not report it. Indeed on a busy Saturday night in most city centres it is best to call the paramedics who will actually turn up (see police response policies). The police seek to control (not prevent) crime by 'operations'. So they divert resources for example currently in Greater Manchester to domestic burglaries. Next quarter the number will go down but not permanently.
Sometimes these operations are very successful as with gun and gangs in Manchester as the current perpetrators are removed from cirulation for a bit... but long term prevention is another story.
So you can draw few conclusions from these figures. The British Crime Survey suggests some mutipliers to turn them into estimates of the actual figures. So the real number of serious assults are three times the number reported to the police.
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22. At 11:25pm on 23 Jan 2009, busby2 wrote:
MonkeyBot5000 wrote that weather affects crimes "especially when you're talking about crimes of opportunity that are committed outdoors. If there are fewer people outdoors, then there are fewer people to commit crimes against".
Quite. But that is not to say that when the weather improves that criminals don't make up for lost time and commit more crimes to make up for lost time!
Which is exactly what the figures show. July 2008 had average weather for the time of year and the number of crimes for that quarter went back up to what would be expected.
The real problem is still the misuse of statistics. There was an unusually low number of crimes in Jul-Sep 2007 and the government is claiming that the return to the normal level in Jul-Sep 2008 is evidence of a massive rise in knife crime.
It's the same reason you often see speed cameras in pointless places. A road has an average of 10 accidents a year, but in one particular year there are 15 accidents. Since there was a 50% increase in the number of accidents, a speed camera gets put up. The next year the number of accidents returns to normal and it's used as evidence that the camera was effective.
In reality, the 15 accidents a year was statistically likely to happen once every ten years. The following year would have seen a reduction in accidents even without the camera as the numbers naturally tended back towards the average.
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Just like to support MonkeyBot2000's point regarding normal random fluctuation. I couldn't agree more, as seen in so many aspects of life. It's sure frustrating when politicians make claims on these bases.
I believe this is a weakness in Mark's evidence. What you'd really need are daily (not seasonal) crime stats (over a year or two, for towns where you can know whether it was likily to be raining on that day). This must be possible (compare figures from the met office (aftercast) and local police forces). Any research students fancy it? Bit difficult to justify i suppose!
Lastly, there is the issue of the police helicopter weather minima, which may factor in somehow, since there's certainly a causal relationship between low cloud and rain!
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But why did total robberies go down?
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I suppose another way to look at this is to question why we should be surprised if it were indeed true?
Isn't weather one of the biggest determinants of behaviour? Does ALL activity simply increase in better weather, including crime. Afterall, D-Day was delayed many times because of rain, international cricket and tennis stop for rain, fewer people spectate at sports (and maybe riot afterwards) rain contributes to major pile ups and death on the roads, and the occasional airline disaster.
Would it not be MORE odd if it had NO effect on crime figures?
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The first problem is in the question asked at the start. If you want this to be a scientifically based investigation then stating the answer before finding the results seems silly. It would be far more credible to state a question such as "What is the relationship between rainfall and knife crime?". From here the independent, dependent and controlled variables could be selected and then the method for collection could be described.
The problem with most politicians and journalists is that they appear to start with the answer and then find the data to support their answer. Ask any sensible scientist if this is good method and most will hopefully say no.
My suggestion to many is to write a better research question in the first place or keep out of using statistics until some understanding of how to use them is attained.
I imagine most other fellow scientists would agree.
Am i making sense?
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This comment was removed because the moderators found it broke the House Rules.
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