THE POISON GARDEN website      Arum maculatum berries on a Cannabis leaf 


This free script provided by JavaScript Kit

Pontifications on Poison

Being some ramblings on events associated with poisonous plants.

Sunday 29th July 2012

I started a recent blog by explaining;

‘When I use a number to support my argument, it is robust, accurate and completely reliable. When you use a number to refute my point it is a statistic and we all know the one about ‘lies, damn lies and statistics’.’

Today, I want to look at two lots of statistics and see if either of them contain numbers.

I don’t doubt the intention of those who produce official surveys. They have a difficult task and, demonstrably, try and improve the quality of their data with each survey. Thus the British Crime Survey (BCS) has become the Crime Survey for England and Wales (CSEW) to reflect what has always been its geographical range. I wish they had gone further, however, and called it the Crime Survey of Households in England and Wales because it is the idea that it is a full survey that leads to the problems.

In addition to its general survey of experience of crime and perceptions about its prevalence, the CSEW surveys illicit drug use on a self-report basis and produces separate documents about what it calls ‘Drug Use Declared’.

There’s another difference this time; the data has been published online with supporting downloadable Excel spreadsheets as well as in a single pdf report. There’s an entry page1 giving details of all the different sections and access (at the bottom of the page) to the pdf.

The way the CSEW works is that interviewers go to a sample of households and ask questions about a variety of matters related to crime. The interviewer then asks if the interviewee is willing to take part in the drug use section and, if they agree, the interviewee is asked to complete a survey on the interviewer’s laptop so that the responses are anonymous.

The drug use section only interviews people in the age range 16 to 59 because there are other ways that drug use by the under 16s is assessed and, the belief is, drug use by over 60s is too rare to make a survey economically justifiable. The Office for National Statistics is responsible for the CSEW but the Home Office extracts and analyses the ‘drug use declared’ information.

Like the terms and conditions for online purchases or software downloads, one of the most important documents of the whole publication, the ‘User Guide’ containing an explanation of the method and giving its limitations2, is unlikely to be read by the majority of those interested in the report as a whole.

That’s unfortunate because it does contain some very significant information that should colour the way the survey is read and used. The User Guide notes;

‘…the CSEW does not cover some small groups, potentially important given that they may have relatively high rates of drug use: notably the homeless and those living in certain institutions such as prisons. Nor, in practice, will any household survey necessarily reach those problematic drug users whose lives are so busy or chaotic that they are hardly ever at home or are unable to take part in an interview.’

In other words, this is a survey of drug use amongst people who are least likely to be drug users.

It is very easy to demonstrate the flaws that arise just by looking at heroin, methadone and crack cocaine use. The CSEW finds that 92,000 people used one or other of these substances in the previous month. It gives a range of 50-142,000 for its estimate. I’ve taken the last month prevalence figures because I think it is fair to assume that problem drug users will come from the population with the highest levels of drug use.

Problem drug users are, of course, of interest to other bodies than just the Home Office. The National Treatment Agency for Substance Abuse (NTA) is part of the National Health Service (NHS) and, according to its ‘About Us’ page ‘was created as a Special Health Authority in 2001 to improve the availability, capacity and effectiveness of drug treatment in England’. As part of its work, it funds combined research by the University of Glasgow and the University of Manchester into what a private company would call its target market.

The NTA publishes the work of the two universities on its site. ‘Estimates of the Prevalence of Opiate Use and/or Crack Cocaine Use, 2009/10’ is the most recent such report.3 This work found that there were an ‘estimated 306,150 opiate and/or crack cocaine users aged 15 to 64 in England in 2009/10’. I’m not comfortable with the estimate being to the nearest one, especially when giving the 95% confidence interval as 299,094 – 316,916, but I’ll settle for 300k, give or take, say, 20k.

Now, the period covered is different and the age range is slightly different but I think we can be fairly sure such differences don’t explain the discrepancy between the NTA’s 300k and the CSEW’s 92k.

Trying to explain the difference gets into more semantic conundrums. The CSEW User Guide talks about the ‘homeless’ but, officially, there are ‘homeless households’, that is households in temporary accommodation. You might expect the CSEW to be able to survey this group but let’s suppose they don’t and that the approximately 60,000 households in temporary accommodation4 at any time are excluded. In addition, estimates suggest around 2,000 people sleep rough in England5. The prison population is no more than 90,000 (based on the September 2010 total of 84,0006)

So the total excluded from the CSEW is around 152,000 (apart from ‘those problematic drug users whose lives are so busy or chaotic that they are hardly ever at home or are unable to take part in an interview’) and if all of them were using opiates or crack cocaine we’d still be around 50k short. Of course, they are not all using. Government figures suggest that less than 10% of prisoners use ‘drugs’ though campaign groups believe the figure is closer to 35%. That would suggest 30k prisoners are using. The highest reported overall prevalence in the world is 2.8% so if we said 10% of the 62k ‘homeless’ were using we’d still be grossly over-estimating.

By these over-estimates, you can get the CSEW’s 92k up to just under 150k, still only half the NTA figure.

I’m not saying the NTA’s figure is completely correct but the actual number of people receiving treatment is much more certain and this is around 200k per year from the NTA’s own figures.

Very clearly, the CSEW is meaningless when it comes to the number of users of opiates and crack cocaine, the substances accepted as leading to almost all problem drug use. It may well be just as meaningless in all other areas.

I’ve had these concerns about the crime survey data for some years but assumed it was something I wasn’t understanding as most people, on all sides of the drug debate, seemed to accept them. I was very pleased, therefore, to see Russell Newcombe point out this discrepancy on Twitter.

Why does this matter? Because these numbers are accepted at face value by most people and policy can be based on them. Even those who may be concerned about the absolute values seem to be willing to accept that the surveys provide a useful measure of trend over time.

I’m not sure they do. In fact, I’m pretty convinced that the Drug Use Declared figures from the CSEW offer nothing of value. I'd be interested to hear your opinion.

In a future piece, I’ll look at what they say about Catha edulis, khat, a substance added to the survey this year.


1. Drug Misuse Declared: Findings from the 2011/12 Crime Survey for England and Wales Home Office 25th July 2012
2. User Guide to Drug Misuse Declared: Findings from the Crime Survey for England and Wales Home Office 25th July 2012
3. Estimates of the Prevalence of Opiate Use and/or Crack Cocaine Use, 2009/10 The National Treatment Agency for Substance Abuse 5th September 2009
4. Homelessness The Poverty Site
5. Number of rough sleepers in England rises by a fifth The Guardian 23rd February 2012
6. Offender Management Statistics Quarterly Bulletin Ministry of Justice January 2011  

Submit a Comment

You are welcome to comment on the above. All comments are pre-moderated and may take some time to appear. This site is aimed at people of all ages so please remember that when writing your comment.


Please provide a valid email address or the site's anti-spam measures will prevent the comment being submitted. Your email address will not be displayed and will not be used for any other purpose.

Email Address:         

 Your comment.


Press the submit button, once, to send your comment. Remember, it will not be sent unless you have provided a valid email address.


Full Entries


Tuesday 25th October 2016
Saturday 20th August 2016
Sunday 6th March 2016
Wednesday 3rd February 2016


Saturday 28th November 2015
Friday 27th November 2015
Monday 17th August 2015
Wednesday 15th July 2015
Friday 26th June 2015
Thursday 25th June 2015
Thursday 30th April 2015
Wednesday 29th April 2015
Wednesday 11th March 2015
Tuesday 3rd March 2015
Saturday 28th February 2015
Sunday 22nd February 2015

November 2014

Monday 24th November 2014
Saturday 8th November 2014

October 2014

September 2014

Wednesday 24th September 2014
Monday 1st September 2014

August 2014

Tuesday 26th August 2014
Saturday 16th August 2014
Tuesday 5th August 2014
Friday 1st August 2014

July 2014

Sunday 27th July 2014
Wednesday 23rd July 2014
Sunday 13th July 2014
Sunday 6th July 2014
Tuesday 1st July 2014

June 2014

Wednesday 25th June 2014
Tuesday 24th June 2014
Sunday 22nd June 2014
Monday 9th June 2014
Wednesday 4th June 2014

May 2014

Monday 26th May 2014
Sunday 18th May 2014
Wednesday 14th May 2014

April 2014

Sunday 13th April 2014
Saturday 5th April 2014
Thursday 3rd April 2014
Tuesday 1st April 2014

March 2014

Monday 31st March 2014
Tuesday 25th March 2014
Friday 21st March 2014
Monday 17th March 2014
Sunday 16th March 2014
Tuesday 11th March 2014
Tuesday 11th March 2014
Thursday 6th March 2014
Wednesday 5th March 2014
Saturday 1st March 2014

February 2014

Thursday 27th February 2014
Monday 24th February 2014
Wednesday 19th February 2014
Monday 17th February 2014
Thursday 13th February 2014
Monday 4th February 2014
Monday 3rd February 2014
Saturday 1st February 2014

January 2014

Thursday 28th January 2014
Thursday 23rd January 2014
Friday 17th January 2014
Wednesday 15th January 2014
Monday 13th January 2014
Thursday 9th January 2014
Tuesday 7th January 2014
Wednesday 1st January 2014

December 2013

Monday 23rd December 2013
Friday 20th December 2013
Tuesday 17th December 2013
Friday 14th December 2013
Thursday 12th December 2013
Sunday 8th December 2013
Wednesday 4th December 2013
Sunday 1st December 2013

November 2013

Friday 29th November 2013
Wednesday 27th November 2013
Tuesday 26th November 2013
Friday 22nd November 2013
Monday 18th November 2013
Friday 15th November 2013
Thursday 14th November 2013
Sunday 10th November 2013
Thursday 7th November 2013
Wednesday 6th November 2013
Friday 1st November 2013

October 2013

Thursday 31st October 2013
Sunday 27th October 2013
Wednesday 23rd October 2013
Monday 21st October 2013
Friday 18th October 2013
Friday 11th October 2013
Wednesday 9th October 2013
Tuesday 8th October 2013
Monday 7th October 2013
Tuesday 1st October 2013

September 2013

Monday 30th September 2013
Saturday 28th September 2013
Friday 27th September 2013
Monday 23rd September 2013
Sunday 15th September 2013
Monday 9th September 2013
Tuesday 3rd September 2013
Sunday 1st September 2013

August 2013

Sunday 8th September 2013
Tuesday 3rd September 2013
Sunday 1st September 2013

Tuesday 27th August 2013
Sunday 25th August 2013
Monday 19th August 2013
Friday 16th August 2013
Tuesday 13th August 2013
Friday 9th August 2013
Friday 2nd August 2013
Thursday 1st August 2013

July 2013

Saturday 27th July 2013
Sunday 21st July 2013
Wednesday 17th July 2013
Monday 15th July 2013
Saturday 13th July 2013
Friday 12th July 2013
Thursday 11th July 2013
Wednesday 10th July 2013
Tuesday 9th July 2013
Saturday 6th July 2013

June 2013

Friday 28th June 2013
Tuesday 25th June 2013
Friday 21st June 2013
Thursday 20th June 2013
Wednesday 19th June 2013
Saturday 15th June 2013
Sunday 9th June 2013
Saturday 8th June 2013
Saturday 1st June 2013

May 2013

April 2013

March 2013

February 2013

January 2013

December 2012

November 2012

October 2012

September 2012

August 2012

July 2012 blog

June 2012 blog

May 2012 blog

April 2012 blog

March 2012 blog

February 2012 blog

January 2012 blog

December 2011 blog

November 2011 blog

October 2011 blog

September 2011 blog

August 2011 blog

July 2011 blog

June 2011 blog


The POISON GARDEN website is not connected with Alnwick Garden Enterprises Ltd and/or The Alnwick Garden Trust.