How Joanna Blythman got it wrong, part 3

As before, throw six to start if you want to know what I think I’m doing here.

After her introduction Joanna Blythman gets stuck in to the issue of ‘consensus’;

As is often the case with the scientific dogmas of the day, the so-called scientific consensus is a lot shakier than it appears… even within the scientific community, indeed on the self-same advisory body, there are dissenting voices.

This should surprise no-one. There is a multitude of research into cannabis and other illicit drugs, of vastly different scope and size — and quality. It would be a great shock if all of this pointed to the same conclusion about harm. Indeed if the evidence was coherent and pointed the same way why would we need the Advisory Council on the Misuse of Drugs (ACMD)? The correct recommendation would be obvious to everyone.

It is an extremely simple matter, therefore, to present some evidence which seems to contradict the consensus view of the ACMD. It’s even easier if you’re not going to appraise the evidence you quote for the robustness of its findings (this is not meant to cast any doubt on the validity of Professor Robin Murray’s longitudinal study, which I will look at in another post). Selectively quoting single items of evidence which give the answer you want to hear doesn’t sound much like healthy scepticism to me — more like the bolstering of a dogma.

The same approach can be seen in this post from Ann Widdecombe. Personally, if I found out I was on the same side of the argument as the Right Irrational Member for Maidstone and the Weald I would take that as a sign to reconsider urgently my position, but I’ll leave that aside for two reasons;

  1. Orwell said that some things are true even though the Daily Express says they are, so it doesn’t pay to be too rigid about those you normally disagree with
  2. I don’t want to damn Blythman simply by the company she keeps, unwittingly or otherwise. I hope to argue reasonably and not resort to a kind of “ad hominem by association”, even though I hope to demonstrate later that Blythman is not above using fallacious arguing techniques such as ad hominem.

It’s worth noting that both Blythman and Widdecombe quote research which supports their position but don’t cite it, so the reader can’t track down the original research to check its validity. This matters because the interpretation given by a newspaper to an article you can’t see could misprepresent or distort it and you wouldn’t be able to tell.

I should point out at this stage that I’m not interested in the Government classification of cannabis per se, which has been done to death in countless other places. What I’m interested in the opportunism which took this row as a pretext to peddle a dreadful article about scientists and health policy in general. So any comments about the relative harms or otherwise of particular drugs are likely to be ignored.

The ACMD examined probably several hundred, possibly a few thousand probably took into consideration hundreds of articles about cannabis.These would have ranged from animal investigations to epidemiological research et cetera. As well as this it listened to oral contributions from interested parties. It assessed all of these for relevance and for the reliability of their findings. At the end of it the Council made a recommendation. It’s fine to disagree with the recommendation, as some within the scientific community have done, but to imagine that flagging up a single piece of evidence means you’ve discredited the whole review is naive in the extreme.


4 Responses to “How Joanna Blythman got it wrong, part 3”

  1. quasilobachevski Says:

    The ACMD examined probably several hundred, possibly a few thousand, articles about cannabis.These would have ranged from animal investigations to epidemiological research et cetera.

    Reference, please! (Since you rightly castigate Blythman/Widdecombe for not giving theirs.)

    • quantsuff Says:

      Fair point, although in fact you’re picking up on my poor writing — I really should have written “probably examined”. I’ll go & fix that.

      Anyway, try here from page 50 onwards — but my estimate was indeed too generous.

  2. Dan Says:

    Even if all the evidence pointed in the same direction, that is that these drugs were not a serious health risk, I doubt it would matter in the debate on illegal drugs. It seems to me more akin to a religion. People have come to believe so strongly that these drugs are bad that as with the tenets of religion they will cling to this belief in the face of overwhelming evidence to the contrary.

    • quantsuff Says:

      A related point of concern is that currently it seems as though saying “well, cannabis causes schizophrenia” (which is a statement that could be examined for a few days in itself) is played as a trump card to close the debate. But we’re talking about cannabis’ position in relation to other drugs of misuse, not about selling it from newsagents. No consideration is given to the relative risk of schizophrenia, the robustness of the case against cannabis, and the relative health risks of the other illicit substances it is being ranked against.
      The psychosis/schizophrenia question is an undoubted extra complication, but it doesn’t close the debate on its own.

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