To point out the obvious, our language (System 2) is more coarse-grained
than our (System 1) experience. Where System 1 deals with all sorts of
conditionals continuously and largely without reflection, when System 2
needs (or thinks it needs) to deal with them, it necessarily simplifies
our experience into manageable (for it) chunks.
As long as we remember that this chunking (modeling) is only a very
rough approximation of our experience (let alone of reality), it can be
useful. This is the case particularly if we remember that while a
satisfactory depiction or explanation of reality is probably not
feasible, the identification of more or less responsible (appropriate,
defensible) actions often is feasible.
One popular form of chunking is to try to express our experience in
binary terms:
E.g., Fact vs. Lie, rather than assessments with greater and lesser
likelihoods of inaccuracy (avoidable or irreducible) and bias (intended
and unintended).
"Asymptomatic" is more interesting; "Symptomatic" isn't quite the other
half of the chunk. Perhaps it is "diseased" (or sick?):
Some real-world definitions of "asymptomatic", listed in approximate
order of the actionability of the information they produce:
1. Didn't volunteer any symptoms thought by the patient or physician to
be potentially related to the condition of interest.
2. Responded negatively when asked by a physician, "Any problems?"
3. Responded negatively to a more or less extensive set of questions
produced ad hoc by a clinician.
4. Responded negatively to a (general or disease-specific; validated or
unvalidated; professionally administered or not) questionnaire (followed
or not by an open-ended interview).
5. When viewed from five (or 10 or 20) years on, there was no
identified recurrence of disease--therefore no symptoms due to the
disease were probably present at one year (regardless of the results of
1, 2, 3, or 4).
Jim
James M. Walker, MD, FACP
Chief Medical Information Officer
Geisinger Health System
The best way to predict the future is to invent it.
- Alan Kay
>>> "Huw Llewelyn [hul2]" <[log in to unmask]> 8/23/2012 11:58 AM >>>
Ben
It all depends on implied definitions again, which is a potential
minefield. If the paper actually defined 'cured' as 'remained
asymptomatic for 1 year after treatment was stopped', it is an
observation, which if not confessed to be a blatant lie, is a fact!
Perhaps it would be better to use the term 'documented observation' for
symptoms, physical signs, test results or combinations of these. I used
'fact' (in the sense that it can be disputed) because it was shorter but
will avoid it in future if there is a better term. The term 'evidence'
seems to be used when the 'documented observation' is used to support a
specified prediction (on which a decision might also be based).
Huw
________________________________
From: "Djulbegovic, Benjamin" <[log in to unmask]>
Date: Thu, 23 Aug 2012 16:29:36 +0100
To: Huw Llewelyn [hul2]<[log in to unmask]>;
[log in to unmask]<[log in to unmask]>
Subject: RE: Definition of evidence
Huw, "all patients in the study given drug x were cured" (as well as
the statement "because all I can see is the level field, the Earth is
flat" (to paraphrase Ahmed's sent in a previous e-mail example) are not
factual statements (=data) as you cannot directly observe "cure", or if
the Earth was flat (back in Middle Age). They refer to inferences to
support given hypothesis (patients are "cured", the Earth is flat),
which is why is commonly said that evidence *points beyond itself*
(to enhance reasonableness or truthfulness of some particular claims").
And, indeed the difficulties agreeing on these issues, is one of the
problems for EBM.
ben
________________________________
From: Huw Llewelyn [hul2] [[log in to unmask]]
Sent: Thursday, August 23, 2012 10:52 AM
To: Djulbegovic, Benjamin; [log in to unmask]
Subject: Re: Definition of evidence
But facts are always being disputed! A fact takes the form of a
proposition and a proposition can be true or false. To assert that
something is a 'fact' (eg that "all patients in the study given drug x
were cured"), usually induces critical listeners to examine its validity
by asking many questions. This is especially so in law, medicine and
science.
To me, "low quality evidence" may refer to observations or 'a fact'
that has a low probability of replication for one reason or another. The
meaning of words vary in different contexts. This is even more apparent
to those who constantly deal with people in different disciplines. I
sympathise with Jon's concern about this and the problems it can cause,
especially when addressing a multi-disciplinary audience.
Huw Llewelyn
________________________________
From: "Djulbegovic, Benjamin" <[log in to unmask]>
Sender: "Evidence based health (EBH)"
<[log in to unmask]>
Date: Thu, 23 Aug 2012 12:35:32 +0100
To:
[log in to unmask]<[log in to unmask]>
ReplyTo: "Djulbegovic, Benjamin" <[log in to unmask]>
Subject: Re: Definition of evidence
A problem of defining evidence as a fact is that fact cannot be false
-facts are by definition true. This is not necessary the case with
evidence - evidence can be false , as we often used in EBM ( eg " low
quality of evidence" to indicate inconsistency with the truth).
A separate issue is "public " vs. "private" evidence, or relation of
definition of evidence to the methods employed.
Some of this is discussed in the article I sent yesterday.
Ben Djulbegovic
Sent from my iPad
( please excuse typos & brevity)
On Aug 23, 2012, at 4:48 AM, "Huw Llewelyn [hul2]"
<[log in to unmask]<mailto:[log in to unmask]>> wrote:
Hi Jon
I can only re-iterate that evidence is a fact that is used to justify a
prediction (which may or may not be verifiable later). The reliabiity of
the facts making up the evidence have to be agreed with the listener or
reader that one wishes to convince. The evidence must therefore be
'recognised' according to rules that promote some degree of
reproducibility.
The degree of reliability demanded of evidence varies between
disciplines and individuals. Some will accept 'grey literature'
especially if that is the only thing available but the certainty of any
prediction will be low. If there are plenty of well documented,
carefully observed, highly reproducible facts, then anything less may be
rejected in that discipline.
However, the uncritical may accept anything and those hostile to a
prediction (eg because of COI) may say that even the best evidence that
supports it is too unreliable to convince them!
Huw
________________________________
From: Jon Brassey
<[log in to unmask]<mailto:[log in to unmask]>>
Date: Thu, 23 Aug 2012 08:00:44 +0100
To: Huw Llewelyn [hul2]<[log in to unmask]<mailto:[log in to unmask]>>
Subject: Re: Definition of evidence
Hi Huw,
The fly in the ointment is how do non research-based documents fit into
things e.g. grey literature, policy documents etc? While these are not
research-based they are deemed 'evidence' (of a sort). So any defintion
(for this particular role) needs to have a broader scope!
BW
jon
On Wed, Aug 22, 2012 at 8:48 PM, Huw Llewelyn [hul2]
<[log in to unmask]<mailto:[log in to unmask]>> wrote:
Jon
There are two issues here - what we see and what others report to us
that they have seen.
What we see for ourselves is a reliable fact and if it is used to make
a prediction then it becomes evidence. When others report what they have
seen we have to assess the probability that we would have seen the same
thing if we had been there.
In other words - What is the probability of replication? If this is
high, then we might use the reported fact as evidence to make a
prediction with a probability that is not quite as high as it would be
if we had made the observation personally.
Huw
________________________________
From: Tom Jefferson
<[log in to unmask]<mailto:[log in to unmask]>>
Sender: "Evidence based health (EBH)"
<[log in to unmask]<mailto:[log in to unmask]>>
Date: Wed, 22 Aug 2012 19:33:48 +0100
To:
[log in to unmask]<mailto:[log in to unmask]><[log in to unmask]<mailto:[log in to unmask]>>
ReplyTo: Tom Jefferson
<[log in to unmask]<mailto:[log in to unmask]>>
Subject: Re: Definition of evidence
Jon, it depends whether you want to separate what is presented or
reported from what really went on. These could be the same, either, or.
Which do you mean?
Best wishes,
Tom.
On 22 August 2012 18:11, Marilyn Mann
<[log in to unmask]<mailto:[log in to unmask]>> wrote:
Similar to the CDC definition:
"What is the nature of the 'evidence' in EBM? We suggest a broad
definition: any empirical observation about the apparent relation
between events constitutes potential evidence."
Guyatt et al. Introduction: The Philosophy of Evidence-Based
Medicine.
http://medicine.ucsf.edu/education/resed/articles/jama11_introduction.pdf
Marilyn Mann
________________________________
From: "Juan Acuna" <[log in to unmask]<mailto:[log in to unmask]>>
To:
[log in to unmask]<mailto:[log in to unmask]>
Sent: Wednesday, August 22, 2012 11:25:45 AM
Subject: Re: Definition of evidence
Hi Jon,
This might help, in the context I believe you want to use the
definition of EVIDENCE. It is the CDC definition:
"evidence is a fact or datum which is used, or could be used, in making
a decision or judgment or in solving a [health] problem"
One reference:
http://heapro.oxfordjournals.org/content/16/3/261.full
Juan
Juan M. Acuņa M.D., MSc., FACOG
Associate Professor Human and Molecular Genetics, Obstetrics and
Gynecology, and Clinical Epidemiology
Florida International University Assistant Vice-President for Clinical
and Community Research
Director Division of Research and Information and Data Coordinating
Center
FIU Herbert Wertheim College of Medicine
Guest Researcher, Centers for Disease Control and Prevention
WHO-PAHO Collaborating Center
11200 SW 8th Street
AHC2 - 474
Miami, FL 33199
Phone (305) 348 0676<tel:%28305%29%20348%200676>
email: [log in to unmask]<mailto:[log in to unmask]><mailto:[log in to unmask]>
________________________________
From: Evidence based health (EBH)
[[log in to unmask]<mailto:[log in to unmask]>]
on behalf of Jon Brassey
[[log in to unmask]<mailto:[log in to unmask]>]
Sent: Wednesday, August 22, 2012 10:56 AM
To:
[log in to unmask]<mailto:[log in to unmask]>
Subject: Definition of evidence
Hi All,
I've been asked to come up with the definition of 'evidence'.
Some background it that it relates to an evidence service that will
work with different types of 'evidence', such as primary research,
secondary research, policy documents and gray literature. The service
will do literatures searches, reviews etc. The definition is seen as
important as we want to make a distinction between other services the
organisations offers e.g. health intelligence!
I imagine there's a definition out there somewhere!
BW
jon
--
Dr Tom Jefferson
www.attentiallebufale.it<http://www.attentiallebufale.it>
--
Jon Brassey
TRIP Database
http://www.tripdatabase.com
Find evidence fast
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