On Capital Punishment

Capital punishment is wrong.  Not because all murderers deserve to live, but because it diminishes us all when the state kills on our behalf.

In the developed world, only the USA carries out judicial executions (the vast majority of the world's executions are in China).  I'm writing about this now because of the attention focussed on the execution of Troy Davis in Georgia on the night of 21st September.

Much of what has been written about it has been assertions of Davis' guilt or innocence of the capital crime he was convicted of.  The crime was committed in 1989 in Savannah, Georgia, at about 1am outside a Burger King restaurant.  One of a group of three young men got into an argument with a homeless man who refused to give him a beer.  Another of the group struck the man with a gun.  A security guard at the restaurant, who happened to be a moonlighting policeman, went to the victim's aid and was shot dead by the assailant.  The identities of the group of three men are not in dispute; the only question is which of them committed the assault and murder.

Perhaps unsurprisingly, polemicists on both sides have wildly exaggerated the strength of their cases.  At the direction of the US Supreme Court, the District Court in Savannah (where the crime was committed) re-examined the evidence in June last year, 21 years after the murder.  This at least makes available a reasonably objective account of what evidence there was, in two parts.

The court account shows that there is no forensic evidence against Davis, and in particular that claims are false that the dead man's blood was found on a pair of   his shorts which were excluded from evidence in Davis's original trial because they had been seized illegally by police.

It shows equally that claims are wildly exaggerated that seven out of nine key witnesses have recanted their testimony.  The two most important witnesses were the homeless man, Larry Young, and his girlfriend who was drinking with him, Harriet Murray.  Young gave an affidavit to the defence saying that his original evidence had been whatever the police wanted.  But the defence declined to call him in person at the 2010 hearing, despite his being present, and despite being warned by the court that his affidavit would carry much less weight if he were not called.  Murray gave a statement to the defence, which she declined to have notarized, largely repeating her original evidence.  There were discrepancies, but nothing approaching a recantation.  She has since died.

Identification evidence is notoriously unreliable.  But the identification in this case is unusual in that it is needed to determine which of the group of young men was which, not to determine who was in the group.  It seems to me that the reliability in general of this sort of identification would be quite easy to test, and that if either side were interested in the truth they would have done the research at some time in the last 22 years.

The Savannah Court's conclusion was "After careful consideration and an in-depth review of twenty years of evidence, the Court is left with the firm conviction that while the State's case may not be ironclad, most reasonable jurors would again vote to convict Mr. Davis of Officer MacPhail's murder".  And it explained at considerable length that it was not the Court's business to conduct a retrial, but to determine whether the original verdict could not reasonably have been arrived at in the light of new evidence.

I don't know what the difference is between "ironclad" and the "beyond reasonable doubt" standard for convictions used in the USA as in the UK.  But I suspect that an expensive legal team has got a lot to do with it.

Rogue Trading at UBS

Having worked for UBS equities for many years, I ought to be writing something intelligent and well-informed about the $2.3bn lost by a rogue trader at the bank.  Reportedly, the trader, Kweku Adoboli, lost the money by buying equity index futures while booking fictitious ETF trades, so that the futures appeared to be hedges for the ETFs.

In fact I am baffled.  First, Adoboli should not have been able to book fictitious client trades (nor genuine ones).  He should certainly not have retained systems access from his previous role in back office.  Second, fictitious trades should have been detected by reconciliation procedures - according to the charges he faces he started doing this in 2008, so there's been ample time to catch up with him.  And third, the Treasury desk will have had to post margin, in cash or securities, on his losing futures positions.  $2bn or so is not a trivial amount (no, really) and they'll have been looking for offsetting margin from the purported client trades.  This should have shown up very quickly.

Which goes to show what I know, since evidently he got round all these obstacles for an extended period...

Bowel Cancer Statistics - update

I've revised the post below, having done some work on the data.

'Three-fold variation' in UK bowel cancer death rates

[I rewrote this post on 19th September, having done further analysis of the data.  The overall conclusion is the same, but better supported by the analysis.  I corrected the penultimate paragraph on 4th October.]

I've copied the title from this BBC story.  The story is an uncritical account of a press release by the charity Beating Bowel Cancer.  "Beating Bowel Cancer calculates that over 5,000 lives could be saved every year".

The press release announces an on-line Bowel Cancer Map which allows one to find the (age-standardized) bowel cancer incidence and mortality for each local authority in England and Scotland.  This is based on 2008 figures provided by UKCIS.  (The raw data are available from UKCIS to registered users only.)

The headline finding is that death rates vary from 9.16 deaths per 100,000 in the semi-rural district of Rossendale (in Lancashire) to 31.09 deaths per 100,000 in the city of Glasgow.  I suppose that the calculation that over 5000 lives a year could be saved is based on reducing the death rate nationally from 17.68 to 9.16 - for a population of 61 million that would save 5,197 lives each year (17.68 is my calculation of the UK-wide death rate, using their data.  They give 17.27 for the death rate in England, and higher figures for Scotland, Wales and Northern Ireland).

But this statistical analysis is completely wrong.  Beating Bowel Cancer didn't reply to a request I sent them for a spreadsheet containing the numbers numbers behind the map, so I've scraped them out by semi-automated postcode query.  The total annual deaths in the data I've got is 15,936 compared with 16,259 reported for 2008 by Cancer Research UK, so I think I've been successful enough in extracting the data.  For a given expected death rate, the actual number of deaths in each district will be a random number sampled from a Poisson Distribution with mean equal to the expected number of deaths in that district.  I assumed that the expected death rate is the same throughout the country, and simulated on a spreadsheet numbers of deaths for every district in the UK. After each simulation, I found the district with the lowest actual death rate in that simulation, and the one with the highest.  The result was that on average the district with the lowest death rate has about 7 deaths per 100,000.  The district with the highest death rate has about 32 deaths per 100,000.  So the observed range - 9 to 31 deaths per 100,000 - is in fact slightly (not significantly) smaller than one would expect if the variation were purely random.  There's nothing in that range to suggest that the expectation is any different from one district to another.

What is happening here is that the analysis has been done over districts that are small enough for random variation to swamp any systematic variation.  Taking this to extremes, one might calculate deaths per household, and find that in the best households no one at all died that year of any cause.  If we could duplicate that for all households, we could all live for ever.

It's worth saying a bit more about the population sizes in each area.  The Bowel Cancer Map doesn't give these numbers directly, but it reports numbers of deaths and "age-standardised" deaths per 100,000.

Age-standardisation adjusts rates to take into account how many old or young people are in the population being looked at. When rates are age-standardised, you know that differences between the local authority areas do not simply reflect variations in the age structure of the populations...

From the data given it is simple to calculate the age-standardized population used for each area.  On this basis, Rossendale has 76,000 people and City of Glasgow has 675,000.  It is not surprising that the lowest death rate is in one of the smaller areas - they are the ones with the greatest random variation.  But if the results are simply random it is surprising that the highest death rate is in a large area.  So I do think that the high death rate in City of Glasgow is not purely random - the Cancer Research UK data confirm that death rates are significantly higher in Scotland.

One more thing.  Adding up the populations for each area, calculated from the deaths and death rates, I get a UK population of 89.75 million.  Since the true figure for 2008 was about 61 million, that's rather surprising.  Doing the same calculation on the data for number of cases, which the map also gives, I get a UK population of 83 million.  The Cancer Research UK table is using a population of just over 61 million, and therefore gets a noticeably higher death rate for about the same number of deaths.  [Update: I find that the CRUK table offers age-standardized rates also: they are very similar to the Beating Bowel Cancer rates.  The heading in the table reads "Age-standardised rate (European)...", so it seems that the standardization is to a European-average age distribution.]

I'm not sure whether I should be railing against the use of stupid statistics in a good cause... 

Making Britain better

There are two policies I advocate to get tough on the causes of riots.

a) Legalize drugs.  Gang culture thrives when stuff people want (alcohol, lotteries, drugs...) is made illegal.
b) Get serious about reducing long-term unemployment.  It disengages people from society (even, or especially, young peoploe facing the prospect of it.).  There are far too few jobs now for unskilled labour.  The way to fix this is to subsidize jobs.  We need a negative income tax for low paid workers.

(a) is almost unanimously agreed among the sort of people who like to talk about this stuff without actually being responsible for it (like me).   I reconsidered it last year when a colleague died in a fall after taking cocaine, leaving a wife and young child.  I would expect legalizing drugs to lead to more people taking them.  Against this, the composition would be much better controlled.  We accept the health risks of alcohol: anything which is not clearly more dangerous should be legal (I suspect that cocaine would not qualify: this is a question to be determined scientifically).

(b) is rather more daring.  I'll write some more about it.

A made-up statistic

I was struck by this statistic in a Spectator article about the riots, written by Harriet Sergeant

A full 63 per cent of white working class boys, and just over half of black Caribbean boys at the age of 14 have a reading age of seven or below.

That is spectacularly implausible, so I went searching for the source.  I found a report titled Wasted published by The Centre for Policy Studies on 27th November 2009, written by the same Harriet Sergeant. (The CPS was founded by Keith Joseph and Margaret Thatcher and describes itself as "one of Britain's leading think tanks".)  The report tells us on page 10:

White working class boys are most at risk of under-performing with 63%  unable  to  read  and  write properly at 14 compared to 43% of white girls from a similar background. Black working class boys do not do much better. Just over half of them, 54%, can not read or write properly at 14.

 That looks like the same statistic, but with a much vaguer description of the underperformance.  But reading on to page 51 (ok, I admit, I didn't actually read it all) we find:

63% of 14 year old white working class boys have a reading ability of half their age. Over half, 54% of 14 year old black Caribbean boys have a reading age of seven

The p10 statistic carries a citation, to "The Daily Mail, 13 August, 2007."  Citing the Daily Mail in a purportedly scholarly paper smacks of desperation, but I ploughed on.  To its credit, that newspaper maintains an on-line archive, in which I found this report on a Bow Group publication

White working-class boys were found to be most at risk of under-performing, with 63 per cent unable to read and write properly at 14.  This compares to 43 per cent of white girls from similar backgrounds and 54 per cent of working-class black boys.

So to the Bow Group (the Bow Group describes itself as "the oldest - and one of the most influential - centre-right Think-Tanks in Britain").  The statistic appears in a table in this document  by Chris Skidmore (then chairman of the Bow Group), written in August 2007.  The document cites this government spreadsheet which contains the same numbers (in "Table 9: Achievements at Key Stage 3 English at Level 5 and above in 2006, by ethnicity, eligibility for free school meals and gender").

Being eligible for free school meals means a child has a parent or carer in receipt of a govenment benefit paid to people on low incomes, so it is talking about the poorest children.  That is not the same as "working class":  57% of the population identifed themselves as working class in a 2007 British Social Attitudes survey, as reported by the BBC.  15% of the boys in the spreadsheet were eligible for free school meals.

The educational achievement in the table is reaching level 5 in Key Stage 3 English.  KS3 is the first three years of secondary-school education (ages 11-14).  Here is an outline of the Key Stage levels : most pupils reach Level 2 by the end of Key Stage 1 (age 7), Level 4 by the end of Key Stage 2 (age 11) and Level 5 or 6 by the end of Key Stage 3.  The assessments in English cover reading and writing, so the data are not specifically about reading.  That aside, if you want to translate failure to reach level 5 into a reading age, you could plausibly describe it as eleven or below.  Which is not what you'd want from your 14-year-old, but is not nearly as bad as "seven or below".

So how did the mostly accurate statistic on page 10 of Harriet Sergeant's 2009 report turn into the tosh in her recent article?  Here's an article by her in the Guardian, published at the same time as her CPS report.

at the age of fourteen, 63% of white working class boys and 55% of black Caribbean boys has a reading age of seven or less

So even at the time she had the wrong statistic from page 51 in her mind.  Furthermore, this government website dated 22nd December 2009  links to the Wasted study and reports it as saying

Almost two thirds (63%) of 14-year-old white working class boys and more than half (54%) of 14-year-old black Caribbean boys have a reading age of seven

I guess that whoever wrote that had their attention drawn to the juicy statistic by someone, very possible Ms Sergeant herself.  I speculate further that in an early version of Wasted the statistic was wrong both times it was used, and someone went through the paper checking the citations and corrected the version with the citation attached.  Either they didn't tell Harriet Sergeant, or they did and she forgot.

There's a clue in the 2007 Daily Mail article to how the confusion first arose: the article starts with a selection of eye-catching statistics, including "at 14, one in five boys has a reading ability of a pupil half his age".  I speculate that this got mixed up from in Harriet Sergeant's mind with the 63% statistic from further down the article.

This statistic has appeared in the Guardian, in Prospect magazine, in the Spectator, and in the last few days in The Telegraph and in a Dominic Lawson article in The Independent.  And it's completely wrong.

Update: repeating my internet searches, I've found this article by Clive Power, casting doubt on various points in the Spectator article, starting with the one investigated here.

UK Income Tax Chart

Here's a chart I made of UK income tax rates in the current year for a person with no special allowances:

The 60% rate at £100,000 appears because the "Personal Allowance" - the zero rate band for low incomes - is progressively withdrawn for incomes above that level.  This was Alistair Darling's idea to get more money out of higher earners without increasing headline tax rates.  George Osborne evinced no pain in adopting the scheme.

This chart includes Class 1 National Insurance payments also - they are levied on employees on a weekly rather than an annual basis: I've assumed full-time employment.

There's another blip in the graph at an annual income of £42,475 where the 40% tax band starts, because the lower National Insurance rate (2% instead of 12%) starts at a slightly higher level.

In a rational world, we would abandon the artificial distinction between Income Tax and National Insurance.  We would determine an appropriate shape for the marginal tax curve - preferably piecewise linear and non-decreasing.  And we would apply a multiplier to the curve to raise what revenue the government deems appropriate.