Michael, That is lovely stuff! However, while I can decipher
"TopGear-speak", I'm still puzzled about the acronymics of
"pseudoKJB language". Would you tell us what "KJB" stand for?
With thanks, and keep up the irony!
Ted.
On 11-Jan-2012 Michael Power wrote:
> Paul
>
> Thanks for your comments, which have provoked some thoughts.
>
> For the time being, I would go with Greg's wording because:
>
> 1. Your wording is technically right, but practically wrong.
>
> 2. Greg's wording may be technically wrong, but it is practically right.
>
> 3. I can't find wording that is both technically and practically correct.
>
> Let me explain.
>
> If you were to mention "Youden index" to an orthopaedic surgeon in a ski
> resort, even a bright one who knows what a numerator and denominator are,
> they would roll their eyes and carry on writing out the request form for a
> routine preoperative chest X-ray for their 20-year old patient with a
> fractured tibia.
>
> However, if you were to quote Greg's 3rd commandment, even your average
> orthopaedic surgeon who doesn't know the difference between a mean and a
> median, might wonder if the X-ray was good for anything other than the
> local health economy.
>
> The reason is that orthopaedic surgeons understand TopGear-speak, and
> related dialects such as pseudoKJB language. (For those of you whose mother
> tongue is not UK English, TopGear-speak uses heavy irony and gross
> exaggeration to amuse the lads and ladettes who have nothing better to do
> than watch Top Gear TV programmes.)
>
> TopGear-speak communicates boring facts and trivial statistics about
> velocity and acceleration to people who have never heard of Newton, let
> alone his laws of motion
>
> Greg's 10 commandments uses pseudoKJB language to communicate boring facts
> about important diagnostic statistics - important as "Thou shalt not kill".
>
> The problem (which orthopaedic surgeons do not have), is that TopGear-speak
> and pseudoKJB language confuse the literal minded and humourless, easily
> annoy the easily annoyed, allow self-promoting politicians to score cheap
> hypocritical points, and draw lurking internet trolls out of their caves to
> be unpleasant.
>
> TopGear-speak works because people understand quantitative-looking
> expressions such as "*99.99% of orthopaedic surgeons are Top Gear fans*",
> not as the ratio 9999/10000, but as the qualitative feeling that almost all
> orthopaedic surgeons are petrolheads.
>
> (If you have followed the argument this far, you can relax, because I have
> come at last to my main point.)
>
> I think that clinicians decide to test, and decide to act on test results,
> on the basis of qualitative thinking and gut feeling, even though
> calculation of Youden indices requires only addition and subtraction, and
> not the third person singular indicative without a lisp.
>
> Our challenge is to get the qualitative, gut feeling, approach based as
> accurately as possible on a sound statistical foundation. To do this we
> have first to understand concepts such as prevalence, sensitivity,
> specificity, predictive values, and Youden index. We then should take the
> next step and see how this can be translated in practical qualitative rules
> of thumb.
>
> Medow and Lucey have a promising approach in their paper "*A qualitative
> approach to Bayes' theorem <http://www.ncbi.nlm.nih.gov/pubmed/21862499>*".
>
> This seems like a great idea. I wonder if it has been tested in practice?
>
> Michael
>
> PS If you are not an orthopaedic surgeon, you should be aware that I have
> resisted the temptation to liberally decorate the above text with metadata
> such as #IronyAlert.
>
> If you are an orthopaedic surgeon, what on earth are you doing here???
>
>
> On 1/10/12, Paul Glasziou <[log in to unmask]> wrote:
>> Dear All,
>> This has been a great idea and discussion to watch :-)
>> However, before spreading further though, its important to get the maths
>> straight.
>> A couple of the items that seem to have problems are:
>> "3. Thou shalt know that if thou dost order a test with a positive
>> predictive value below 50%, thou mightest as well toss a coin."
>> That's incorrect for several reasons. A test may be *very* useful even
>> with a low PPV - if the negative predictive value is good, and that is
>> what is needed.
>> For example, the Ottawa Ankle rule is a very sensitive "test" for
>> fractures*, so negative results rule out (SnNout). But the Rule is not
>> very specific, so the positive predictive value is generally less than
> 50%.
>> That still seems a useful test - saving around 25% of ankle Xrays - but
>> with weak PPV.
>> A "coin toss" is indeed a useless test - but that does not mean a PPV
>> less than 50%, but that the pre-test and posi-test probabilities are the
>> same. That is the predictive value positive would be the same as the
>> pre-test probability - which may be above or below 50% depending on
>> clinical circumstances.
>> So how can you pick a useless test? Two ways to tell are: if the Youden
>> Index (= 1 - (sensitivity + specificity) ) is zero or (equivalently) the
>> (diagnostics) Odds Ratio is 1 (as hence both LR+ and LR- will also be 1).
>> So 3 might read something like:
>> "3. Thou shalt know that if thou dost order a test with a Youden Index
>> near 0, thou mightest as well toss a coin."
>>
>> There is a related problem with Commandment 4:
>> "4 ... Thou shalt recognise that in a low-prevalence population, even a
>> very sensitive test hath poor predictive value, and if thou shouldest
>> order such a test, thou mightest as well toss a coin."
>> Again if we are interested in ruling out, then we might us the sensitive
>> test (SnNout) in low prevalence populations. For example, using highly
>> sensitive d-dimer to rule out PE in someone with a some suspcion, but
>> low probability, of PE.
>> Incidentally, prevalence matters most when tests are only modestly
>> accurate. For a perfect test (100% sensitive and specific) prevalence
>> becomes almost irrelevant. And for either SpPin (100% specific) or
>> SnNout (100% sensitive), then its of low relevance for the +ve or -ve
>> results respectively.
>>
>> Happy Commandment making ;-)
>> Paul
>> * see BMJ. 2003 Feb 22;326(7386):417.
>>
>>
>>
>> On 1/10/2012 2:00 AM, Ash Paul wrote:
>>> Dear colleagues,
>>>
>>> Here's the corrected draft, with grateful help received from Ms
>>> Catherine Ebenezer:
>>>
>>> 1. Before thou dost order a test, thou shalt remember that “All tests
>>> can do harm. Many tests do good. Some tests do more good than harm”.
>>> 2. Thou shalt know the predictive positive value and predictive
>>> negative value of the test before thou dost order it.
>>> 3. Thou shalt know that if thou dost order a test with a positive
>>> predictive value below 50%, thou mightest as well toss a coin.
>>> 4. Thou shalt know the prevalence of the disease in the population
>>> from which the person thou art going to test cameth; for combined with
>>> positive predictive value or negative predictive value, thou canst
>>> then ensure that thou hast interpreted the result properly. Thou shalt
>>> recognise that in a low-prevalence population, even a very sensitive
>>> test hath poor predictive value, and if thou shouldest order such a
>>> test, thou mightest as well toss a coin.
>>> 5. Thou shalt know exactly what thou mightest do with the result of
>>> the test before thou dost order it. “If thou knowest not what thou
>>> shouldest do with the result, or if the test be not part of an
>>> evidence-based pathway, then shalt thou DESIST from ordering such a
>>> test.”
>>> 6. Thou shalt know the cost of the test thou intendest to order,
>>> before thou dost order it, and also thou shouldest enquire whether
>>> there be cheaper ways of finding the same result.
>>> 7. Thou shalt know whosoever else hath in the past ordered, or might
>>> in the future order, the same test under the same set of
>>> circumstances, and then shalt thou ensure that they know that they do
>>> but waste resources, since thou hast performed the same already
>>> before. Therefore, thou shalt record the result of the test which thou
>>> dost order very clearly that all others might see it.
>>> 8. Thou shalt inform patients that “shinier scanners and swizzier
>>> kits" might well give better resolution pictures, but might not
>>> actually change a clinical management decision.
>>> 9. Thou shalt simply not ask or order patients to undertake diagnostic
>>> tests for which there be no proven evidence of benefit.
>>> 10. Thou shalt explain to the patient, clearly and without bias, that
>>> which the test can and cannot tell thee, and thou shalt ask them if
>>> they are content to proceed in such wise.
>>> Regards,
>>>
>>> Ash
>>>
>>> ********
>>>
>>> ------------------------------------------------------------------------
>>> *From:* Evidence based health (EBH)
>>> [mailto:[log in to unmask]] *On Behalf Of *Ash Paul
>>> *Sent:* 09 January 2012 13:22
>>> *To:* [log in to unmask]
>>> *Subject:* Re: Ten commandments for testing
>>> Dear Greg,
>>> I have biblified yours/Anna's list and circulated it to our NHS
>>> Public Health Commissioners e-group. I have proposed calling them
>>> the Fell-Sayburn Commandments
>>>
>>> 1. Before thou ordereth a test, thou shalt remembereth that
>>> “All tests can doeth harm. Many tests doeth good. Some tests
>>> doeth more good than harm”
>>>
>>> 2. Thou shalt knoweth the predictive positive value and
>>> predictive negative value of the test before thou ordereth it
>>>
>>> 3. Thou shalt knoweth that if thou ordereth a test with a
>>> positive predictive value below 50%, thou might as well
>>> tosseth a coin
>>>
>>> 4. Thou shalt knoweth the prevalence of the disease in the
>>> population from which the person thou art going to test
>>> cometh from; for combined with positive predictive value or
>>> negative predictive value, thou can then ensureth that thou
>>> hast interpreted the result properly. Thou shalt recogniseth
>>> that in a low prevalence population, even a very sensitive
>>> test has poor predictive value, and if thou ordereth such a
>>> test, thou might as well tosseth a coin.
>>>
>>> 5. Thou shalt knoweth exactly what thou art going to doeth with
>>> the result of the test before thou ordereth it. “If thou
>>> doth not know what to doeth with the result, or if the test
>>> is not part of an evidenced-based pathway, then thou shalt
>>> DESIST from ordering such a test.”
>>>
>>> 6. Thou shalt knoweth the cost of the test thou art going to
>>> ordereth, before thou ordereth it, and also enquireth
>>> whether there are cheaper ways of finding the same result.
>>>
>>> 7. Thou shalt knoweth who else might have in the past, or might
>>> in the future, ordereth the same test under the same set of
>>> circumstances, and then ensureth they know they are wasting
>>> resources as thou hast done it already before. Therefore,
>>> thou shalt recordeth the result of the test thou ordereth
>>> very clearly for all others to see.
>>>
>>> 8. Thou shalt informeth patients that “shinier scanners and
>>> swizzier kits" might well giveth better resolution pictures
>>> but they might not actually changeth a clinical management
>>> decision
>>>
>>> 9. Thou shall simply not asketh or ordereth patients to
>>> undertake diagnostic tests for which there is well proven
>>> evidence of no benefit
>>>
>>> 10. Thou shalt explaineth to the patient, clearly and without
>>> bias, what the test can and canst tell thou, and thou shalt asketh
>>> them if they are happy to goeth ahead on that basis.
>>> Regards,
>>>
>>> Ash
>>>
>>>
>>> ------------------------------------------------------------------------
>>> *From:* Fell Greg <[log in to unmask]>
>>> *To:* [log in to unmask]
>>> *Sent:* Monday, 9 January 2012, 12:19
>>> *Subject:* Re: Ten commandments for testing
>>> accept the need for a “full” version (with refs and all
>>> that)….guess it depends on intended audience and endpoint. I
>>> feel the slightly humerous biblified version might have more
>>> “reach” (on account of the humour factor)….but accept that
>>> “reach” and “influence” might be two slightly different things.
>>> I am not going to die in a ditch about either.
>>> The important thing is that the list sees the light of day
>>> outside this e group – published / blogged / other. I am
>>> intending on using it extensively locally.
>>> Do colleagues feel this is publishable.
>>> gf
>>>
>>
>>
>> --
>> Paul Glasziou
>> Bond University
>> Qld, Australia 4229
>>
>>
----------------------------------
E-Mail: (Ted Harding) <[log in to unmask]>
Date: 11-Jan-2012
Time: 10:45:03
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