Why is the Bayesian method not employed for diagnosis in practice

Tom Benzoni benzonit at GMAIL.COM
Wed May 30 18:08:48 UTC 2018


I think there may be sone fundamental misunderstandings of Bayes' theorem
and its application.
The Wiki entry on the topic is quite good.
Tom

On Wednesday, May 30, 2018, Jain, Bimal P.,M.D. <BJAIN at partners.org> wrote:

> The reservation I have about the Bayesian method is about considering a
> prior probability which is a frequency in a population to be prior evidence
> for a disease in a given patient. This notion may make us not suspect a
> disease if its prior probability is low leading to a diagnostic error.
>
> It is of interest that in the two examples given by Dr. Elias, the
> presence of a disease is assessed in terms of a likelihood ratio, and not a
> prior probability. For example, IBS being more likely than splenic artery
> aneurysm given the GI symptoms means that the likelihood ratio of IBS is
> high compared to aneurysm.
>
> Similarly, the likelihood ratio of viral illness is high compared to strep
> throat given the nasal and respiratory symptoms.
>
> What these likelihood ratios are, I do not know, but they may be high
> enough, that further testing may not be required.
>
> Another example of a high likelihood ratio  for a disease is that for
> herpes zoster, given unilateral, blistering skin lesions in a dermatomal
> distribution which does not require further tests for a diagnosis.
>
> In diagnosis, in which our goal is accurate determination of a disease in
> a given patient, evidence from which we diagnose a disease is represented
> by a likelihood ratio as it represents a change in probability ( odds ) of
> a disease in a given patient , locating evidence in this particular patient.
>
> A probability, being a frequency in a population locates evidence in a
> population. Therefore, an inference from a probability  is made in a field
> such as life insurance business in which the goal is long run accuracy with
> tolerance for errors in some individual persons.
>
> I have never come across a diagnosis being made purely from a probability
> in the absence of data with significantly high likelihood ratio in
> published case discussions or in practice.
>
> There seems to be a general impression that evidence in an uncertain
> situation can only be represented by a probability and an inference made
> from it alone. This is not true, as there is flourishing school of
> inference from likelihood alone as seen in books by AWF Edwards, Richard
> Royall, Y. Pawitan and many more authors.
>
> A positive CT study for appendicitis has a likelihood ratio of 19, about
> the same for positive CT angiogram for pulmonary embolism. In practice,
> this study should allow us to diagnose appendicitis definitively with a
> high degree of accuracy in any patient, regardless of prior probability.
>
> It would be of interest to know the diagnostic accuracy of this test
> result across patients with varying prior probabilities  similar to the
> diagnostic accuracy of acute Q wave and ST elevation EKG changes for acute
> myocardial infarction being 85 percent in patients with varying prior
> probabilities.
>
>
>
> Bimal
>
>
>
> *From:* Elias Peter [mailto:pheski69 at GMAIL.COM]
> *Sent:* Sunday, May 27, 2018 12:12 PM
> *To:* IMPROVEDX at LIST.IMPROVEDIAGNOSIS.ORG
> *Subject:* Re: [IMPROVEDX] Why is the Bayesian method not employed for
> diagnosis in practice
>
>
>
> *        External Email - Use Caution        *
>
> I find the proposal that Bayesian analysis is not (or should not be) part
> of the initial diagnostic approach puzzling. The following examples
> illustrate why I feel that way:
>
>
>
>    - The 30-year old who presents with 2 years of intermittent left upper
>    quadrant pain and fluctuating bowel habits is more likely to have irritable
>    bowel syndrome than splenic artery aneurysm. One would not start evaluation
>    with imaging the LUQ.
>    - The 8-year old with 4 days of runny nose, cough and sore throat is
>    so much more likely to have a viral illness than a strep throat that a
>    throat culture is poor medical practice.
>
>
>
> Peter Elias, MD
>
>
>
>
>
> On 2018.05.27, at 8:53 AM, Bruno, Michael <mbruno at PENNSTATEHEALTH.PSU.EDU>
> wrote:
>
>
>
> Thanks Dr. Bimal for starting this interesting thread, and to Stefanie Lee
> for sharing that excellent 2006 paper from Blackmore, *et al.,* as well
> as to Dr. Oldham for his insightful comments.
>
>
>
> I think the Blackmore paper is really touching on the topic of "signal
> detection theory," which is a very useful tool to understand about how
> useful information is actually extracted from complex data sets (like CT
> scans) that have extremely high levels of uncertainty built-in. We
> radiologists practice in a milieu of extraordinarily high undertainty, as I
> noted in my 2017 review in our Society's official journal, *Diagnosis* (DOI
> 10.1515/dx-2017-0006), so this is particularly relevant to us.
>
>
>
> I've attached an excellent PDF discussion of signal-detection theory as
> applied to diagnostic radiology to this message for anyone who might be
> interested.  While radiologists and others may recognize the use of ROC
> curves, which are a feature of this theory, they may not be as familiar
> with the concepts of d', a quantitative measure of how well the
> alternatives can actually be discriminated from the test, and the concept
> of "criterion," whereby the interpreter decides how sensitive *vs*.
> specific they wish to be.  This was the thrust of the Blakemore article,
> and his meta-analysis suggested that radiologists by-and-large got it
> right.  (For David Meyers--the attached PDF is in the public domain,
> provided by Professor David Heeger of NYU).
>
>
>
> Dr. Oldham also got it right, of course, saying that Baysean reasoning is
> not everything in diagnosis, but I believe that it takes us *most of the
> way*.  I very much appreciate Dr. Oldham's analogy that the radiologist
> is acting as the "expert witness" in a courtroom setting while the treating
> physician and patient / patient's family serves as the judge and jury, who
> are charged with ultimately deciding what "truth" is.
>
>
>
> Have a terrific Memorial Day Weekend, everybody!
>
>
>
> Mike
>
>
>
>
> ------------------------------
>
> *From:* James Oldham <james.oldham at HEALTH.NSW.GOV.AU>
> *Sent:* Sunday, May 27, 2018 1:49 AM
> *To:* IMPROVEDX at LIST.IMPROVEDIAGNOSIS.ORG
> *Subject:* Re: [IMPROVEDX] Why is the Bayesian method not employed for
> diagnosis in practice
>
>
>
> Dear all
>
> There is a difference between the treating doctor who makes a
> probabilistic diagnosis and evidence providers such as radiologists who
> comment on phenomena the observe and interpret it - taking Bayesian prior
> probability calculations explicitly into their offerings. I think the
> testing physician and their patients and family as a collective Judge
> relying on evidence provided by expert witnesses. So this final stage will
> be informed by Bayesian logic but not ruled by it and certainly not trying
> to make a prediction- just best information to hand
>
> James Oldham
>
> Child Psychiatrist
>
> NSW
>
> From James Oldham - sent from my phone. (Please accept apologies odd
> sentence construction and creative additions courtesy of Apple autocorrect)
>
>
> On 27 May 2018, at 13:25, Stefanie Lee <stefanieylee at GMAIL.COM> wrote:
>
> An interesting paper from Blackmore and Terasawa, JACR 2006 on the
> complexity of CT interpretation and how clinical probability may be
> factored into the decision to call a test result positive or negative:
>
> "In this paper, we present an example of how health utility assessment can
> be used to guide the optimum interpretation of an imaging test."
>
>
> "Radiologists have the ability to alter the sensitivity and specificity of
> their interpretations. For objective positivity criteria, different
> thresholds can be chosen to consider test results positive. For example,
> with appendicitis, one important factor in CT interpretation is the size of
> the appendix. Using a lower size threshold (eg, 6 mm) to consider an
> appendix abnormal will result in higher sensitivity for appendicitis, at
> the expense of lower specificity. Using a higher size measurement to
> consider the appendix abnormal (eg, 8 mm) would result in lower sensitivity
> but higher specificity. For subjective criteria such as periappendiceal fat
> stranding, the process is the same but less explicit. Individual
> radiologists can alter how much increase in the density of the fat is
> necessary to be considered abnormal “stranding.”"
>
> "In general, when a disease is rare and there are substantial costs to a
> false-positive diagnosis, interpreting a test with high specificity will
> maximize patient benefit. In contrast, when a disease is common and there
> are substantial costs for a false-negative diagnosis, interpretation at
> high sensitivity will maximize utility."
>
> "Our prior meta-analysis indicated that radiologists interpret CT scans
> with approximately equal sensitivity and specificity. The current analysis
> indicates that this is an appropriate threshold at the intermediate
> probability of disease at which CT is commonly used today. If CT is to be
> used in populations at higher or lower probabilities of disease, then
> different imaging thresholds will be appropriate."
>
>
>
> On 15 May 2018 at 13:18, Jain, Bimal P.,M.D. <BJAIN at partners.org> wrote:
>
> In this attached paper, I discuss that the prescribed Bayesian method is
> not employed for diagnosis in practice because probability of a diseases is
> considered evidence for it in a given patient in this method, which is
> incorrect as a probability is a frequency in a population. This leads to
> all sorts of errors in practice which I discuss.
>
> The correct method of diagnosis, which is employed in practice, consists
> of hypothesis generation and verification in which evidence is assessed by
> a likelihood ratio which locates it in the given patient of interest.
>
> Please review and comment on this paper.
>
>
>
> Thanks
>
>
>
> Bimal
>
>
>
> Bimal P Jain MD
>
> Northshore Medical Center
>
> Lynn MA 01904.
>
> The information in this e-mail is intended only for the person to whom it
> is
> addressed. If you believe this e-mail was sent to you in error and the
> e-mail
> contains patient information, please contact the Partners Compliance
> HelpLine at
> http://www.partners.org/complianceline . If the e-mail was sent to you in
> error
> but does not contain patient information, please contact the sender and
> properly
> dispose of the e-mail.
>
>
> ------------------------------
>
>
>
> To unsubscribe from IMPROVEDX: click the following link:
> http://list.improvediagnosis.org/scripts/wa-IMPDIAG.exe?
> SUBED1=IMPROVEDX&A=1 or send email to: IMPROVEDX-SIGNOFF-REQUEST@
> LIST.IMPROVEDIAGNOSIS.ORG
>
> Visit the searchable archives or adjust your subscription at: http://list.
> improvediagnosis.org/scripts/wa-IMPDIAG.exe?INDEX
> Moderator:David Meyers, Board Member, Society for Improving Diagnosis in
> Medicine
>
> To learn more about SIDM visit:
> http://www.improvediagnosis.org/
>
>
>
>
> ------------------------------
>
>
>
> To unsubscribe from IMPROVEDX: click the following link:
> http://list.improvediagnosis.org/scripts/wa-IMPDIAG.exe?
> SUBED1=IMPROVEDX&A=1
>
> or send email to: IMPROVEDX-SIGNOFF-REQUEST at LIST.IMPROVEDIAGNOSIS.ORG
>
> Visit the searchable archives or adjust your subscription at: http://list.
> improvediagnosis.org/scripts/wa-IMPDIAG.exe?INDEX
>
>
> Moderator:David Meyers, Board Member, Society for Improving Diagnosis in
> Medicine
>
> To learn more about SIDM visit:
> http://www.improvediagnosis.org/
>
> <Signal Detection Theory.pdf>
>
>
>
>
> ------------------------------
>
>
>
> To unsubscribe from IMPROVEDX: click the following link:
> http://list.improvediagnosis.org/scripts/wa-IMPDIAG.exe?
> SUBED1=IMPROVEDX&A=1
>
> or send email to: IMPROVEDX-SIGNOFF-REQUEST at LIST.IMPROVEDIAGNOSIS.ORG
>
>
>
> Moderator:David Meyers, Board Member, Society for Improving Diagnosis in
> Medicine
>
> To learn more about SIDM visit:
> http://www.improvediagnosis.org/
>
> ------------------------------
>
>
> To unsubscribe from IMPROVEDX: click the following link:
> http://list.improvediagnosis.org/scripts/wa-IMPDIAG.exe?
> SUBED1=IMPROVEDX&A=1 or send email to: IMPROVEDX-SIGNOFF-REQUEST@
> LIST.IMPROVEDIAGNOSIS.ORG
>
> Moderator:David Meyers, Board Member, Society for Improving Diagnosis in
> Medicine
>
> To learn more about SIDM visit:
> http://www.improvediagnosis.org/






Moderator: David Meyers, Board Member, Society to Improve Diagnosis in Medicine


HTML Version:
URL: <../attachments/20180530/70932804/attachment.html>


More information about the Test mailing list