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Data or Dogma?

Discussion in 'General ME/CFS News' started by Daisymay, Aug 18, 2014.

  1. Daisymay

    Daisymay Senior Member

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    http://www.meactionuk.org.uk/Data-or-Dogma.htm


    Data or Dogma?

    Margaret Williams 16th August 2014



    AndyPandy, Tito, Valentijn and 2 others like this.
  2. Snow Leopard

    Snow Leopard Senior Member

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    While some interesting points are made, I cannot help but think the whole article could be communicated a bit more effectively. Few except perhaps those already convinced of MW's point are going to read all 4000 words.

    Rather than 4000 words, perhaps 400 words with some appendices for any additional background.

    I'm saying this as I'd like to see a wider audience.
    MeSci, alex3619 and Sasha like this.
  3. Sasha

    Sasha Fine, thank you

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    I haven't read this particular paper yet but I think that there's a general tendency in authors who do all this hard work for us to document things in very great detail without providing a short overview that is likely to actually be read. People - especially PWME, busy doctors, and people who hold the opposing view aren't going to read anything long.

    It's actually pretty hard and skilled work to produce something concise. It's an extra job once you've gathered all the info, but as you say, @Snow Leopard, it's important to do it if you want a wider audience.
    WillowJ and MeSci like this.
  4. alex3619

    alex3619 Senior Member

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    This problem with detail/brevity I hope to address in my book. Margaret Williams will look short compared to what I am hoping to do. However I hope to thematically structure it, then provide detailed summaries and introductions, and publish the summaries separately as a more readable text, from which someone can go to my book for more substantiating detail, topic by topic as it interests them. We need the capacity to see both the forest and the trees.

    I am also considering an alternative structure entirely, but its all on hold for now.
    MeSci likes this.
  5. A.B.

    A.B. Senior Member

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    Could someone explain this in plain English?
  6. Bob

    Bob

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    I'm not a statistician, but I think that's an incorrect interpretation of the "standard error of the mean".
    In simplistic terms, I think the "standard error of the mean" indicates how precisely the mean is known, so that as a sample size becomes larger, the "standard error of the mean" becomes lower, and the figure given for the mean is considered more reliable.
    The "standard error of the mean" is not used to define normal ranges, as far as I understand.

    A mean SF-36 physical function score of roughly 95 for healthy individuals is commonly reported.
    The PACE trial used a mean score of 84 as a population norm, to define the normal range, and recovery, however their mean score included people with chronic illness and adults of all ages. Their method of defining a normal range was inappropriate for a number of reasons, as indicated by the fact that a participant could theoretically have a worse physical function score after treatment (with CBT/GET) and then be declared 'recovered'.
    Last edited: Aug 19, 2014
  7. alex3619

    alex3619 Senior Member

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    The net effect of the PACE claim for normal range is they are claiming that its normal for a twenty year old to have the functional capacity of an average (not especially well or fit) eighty year old. Who in their right mind would accept that claim? They are hiding behind the problem that most people do not look up the appropriate reference ranges, and behind an erroneous use of statistics.
    Valentijn likes this.
  8. MeSci

    MeSci ME/CFS since 1995; activity level 6

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    What I take from this last bit - which I don't think was very well-worded - is that the control patients all had a physical function of 93.5 or more. The standard error of 1.5, with a mean of 95.0, means that it ranged from 93.5-96.5 (1.5 lower and 1.5 higher than 95.0).

    So if (any of) the patients scored less than 93.5, they were worse than any of the controls.

    I think I got that right!
  9. Bob

    Bob

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    @MeSci, I think you aren't a statistician either? :)
    I don't think your interpretation is right.
    The standard error of the mean indicates the reliability of the mean.
    It does not indicate the range of values that were used to calculate the mean.
    Valentijn likes this.
  10. MeSci

    MeSci ME/CFS since 1995; activity level 6

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    Oh dear. I have admitted elsewhere that stats are my weak point! :redface:
    Bob likes this.
  11. alex3619

    alex3619 Senior Member

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    Its probably easier to think of it as 95 plus or minus 1.5. Old school use of plus and minus. Stats are also a weak point for me - I understand some of the underlying principles, but I am definitely not statistically minded.
    Bob likes this.
  12. MeSci

    MeSci ME/CFS since 1995; activity level 6

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    So I was right? :confused: Or are you saying that the mean is between 93.5 and 96.5 rather than the range of values is? My brain hurts...maths always does that to it. My brother got all the maths genes.

    (I thought that reliability was indicated by the 'p='/'p<' value.)
  13. Bob

    Bob

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    Yes, that's what Alex means. I don't think it's a precise explanation, but it's a good way of understanding it.

    lol, I think my sister would sympathise with you there! :)

    "The P value gives the probability of any observed difference having happened by chance."

    That's my best explanation. Over to someone else if you need a better explanation!

    Look at the third result in this google search list (i.e. the PDF), if you'd like to see a very helpful, and easy-to-understand book re medical stats:
    https://www.google.co.uk/search?q=medical statistics made easy harris taylor&sourceid=ie7&rls=com.microsoft:en-GB:{referrer:source}&ie=UTF-8&oe=&rlz=1I7GZAZ_en&gws_rd=ssl
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  14. MeSci

    MeSci ME/CFS since 1995; activity level 6

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    Yes - that's what I understood about it. I did have to do stats for my degrees, but it took very hard work and brain exhaustion (I already had ME a year into the first degree). The maths was my least favourite part of my science studies as I find it so hard.

    Thanks for the link, but I won't be able to retain the info. Brain says no! I'll leave it to you stats wizzes.
    Bob likes this.
  15. alex3619

    alex3619 Senior Member

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    I think that like many things in statistics, things like the plus minus explanation are approximations, as its involves probabilities. Its a calculated probability range, not a certainty.

    Probability is not intuitive. In a recent test of people who used statistics every day, namely economists, 97% failed a basic grasp of probability in the real world. Our brains are really bad at intuitively grasping this stuff, which is why we have math. Yet the math has to be translated to and from the real world, and this is where it often goes horribly wrong.
    ahimsa, WillowJ and MeSci like this.
  16. alex3619

    alex3619 Senior Member

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    My understanding is also that the P value is not always accurate. Its, again, a calculated probability and uses assumptions that are not always valid. I forget nearly all the explanations for this kind of stuff, my brain does not retain it and I have to relearn it again and again. Grrr ....

    Further, let us recall that not likely being due to chance does not rule out it being due to bias, fraud, etc. Chance is just one risk, so is bias and fraud and just bad methodology. With publication bias causing increased publication of positive findings, this is a huge one to consider and is external to any study. So it is not even reflected in the P value.
  17. Leopardtail

    Leopardtail Senior Member

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  18. Leopardtail

    Leopardtail Senior Member

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    The 'Quick overview' is really the job of the abstract @Sasha - If the paper itself is too short or does not give convincing detail, it's nor really of much use to other academics and can neither be challenged, nor confirmed.
    Sasha likes this.
  19. Sasha

    Sasha Fine, thank you

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    You don't generally see abstracts outside of academic papers published in scientific journals (although you might see something similar referred to as an executive summary). I think that if we want to do a good job of persuading people, though, we've got to have some sort of concise overview.
    MeSci likes this.
  20. Leopardtail

    Leopardtail Senior Member

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    Basically the statistical term 'sample mean' is not 'the mean of the sample' but the mean of multiple variables each of which itself is a mean. Lets call those variable Member_Means [1..x]

    Standard error comes in because each of those separate variables (Member_Mean [1..x] ) may not average the same number of samples. Standard Error is a standard deviation not of the values but of the number of samples in each value.

    E.g. mean 1 = 25 [contains 5 samples]. mean 2 = 25 [contains 1 sample] mean 3 = 10 [contains 2 samples]
    True mean is 21.25
    Sample mean is 20

    Standard Error is the standard deviation of the set 5,1,2 that being 1.7
    It's a guess about how likely to the data is to be wrong when attempting to combine averages simply.

    In this case it does look wrong..
    WillowJ likes this.

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