I am wondering whether it may be important to consider sample size relative to the prevalence of a given condition in the general population. If one is studying the effects of an intervention, for example, on individuals with a rare disorder or on individuals with a specific set of co-morbidities or case-mix factors, then a study of only 75 patients could be considered to have greater external validity than a similar study focusing on a highly prevalent condition that included 10,000 patients. Classifying studies based solely on sample size does not seem to adequately convey how well the findings can be generalized to the population of affected individuals unless somehow the prevalence of the condition is also considered. But perhaps Jon, you are not considering this classification scheme as a way to estimate how valid it is to generalize a study's findings to the larger population.
-----Original Message-----
From: Evidence based health (EBH) [mailto:[log in to unmask]] On Behalf Of Matt Williams
Sent: Thursday, June 06, 2013 2:58 AM
To: [log in to unmask]
Subject: Re: EVIDENCE-BASED-HEALTH Digest - 4 Jun 2013 to 5 Jun 2013 (#2013-141)
Dear Jon,
My feeling would be to use (something like) the log of the study size. Alternatives would be square-root, etc. These would give you fewer values (few studies are > 10e6), and capture the fact that adding 100 pts to a trial has more of an impact if you already have 100 rather than 1000.
In theory, there should be an empirical basis for this - you might try relating it to the formula(e) used for sample size calculation, but I don't have those to hand. I've been meaning to look at this for ages, and have never got round to it.
Hope that's useful,
Matt
Sent from my BlackBerry® wireless device
-----Original Message-----
From: EVIDENCE-BASED-HEALTH automatic digest system <[log in to unmask]>
Sender: "Evidence based health (EBH)" <[log in to unmask]>
Date: Thu, 6 Jun 2013 00:24:38
To: <[log in to unmask]>
Reply-To: "Evidence based health (EBH)" <[log in to unmask]>
Subject: EVIDENCE-BASED-HEALTH Digest - 4 Jun 2013 to 5 Jun 2013 (#2013-141)
There are 10 messages totaling 2986 lines in this issue.
Topics of the day:
1. Categorising the size of a clinical trial (10)
----------------------------------------------------------------------
Date: Wed, 5 Jun 2013 17:10:31 +0100
From: Jon Brassey <[log in to unmask]>
Subject: Categorising the size of a clinical trial
Hi All,
This is a strange question, but would welcome any advice. I'm trying to create a system to categorise the size of trials, based on the number of participants. I'm thinking it'd be something like very small, small, medium, large and very large.
I could arbitrarily say something like:
- very small trial = less than 20 patients
- small = 21-99
- medium = 100-499
- large = 500-4999
- very large = 5000+
But, is there already some work in this area?
BW
jon
--
Jon Brassey
Trip Database
http://www.tripdatabase.com
Find evidence fast
------------------------------
Date: Wed, 5 Jun 2013 16:37:55 +0000
From: "Dahm,Philipp" <[log in to unmask]>
Subject: Re: Categorising the size of a clinical trial
Hello Jon:
I am curious – what is your purpose for categorizing trials by sample size?
Ph*
Philipp Dahm, MD, MHSc, FACS
Professor of Urology, University of Florida Coordinating Editor, Cochrane Prostatic Diseases & Urological Cancers Group College of Medicine, Health Science Center Box 100247, Room N2-15 Gainesville, FL 32610-0247
Phone: (352) 273-8634
Fax: (352) 273-7515
Email: [log in to unmask]
From: Jon Brassey <[log in to unmask]<mailto:[log in to unmask]>>
Reply-To: Jon Brassey <[log in to unmask]<mailto:[log in to unmask]>>
Date: Wednesday, June 5, 2013 12:10 PM
To: Evidence health <[log in to unmask]<mailto:[log in to unmask]>>
Subject: Categorising the size of a clinical trial
Hi All,
This is a strange question, but would welcome any advice. I'm trying to create a system to categorise the size of trials, based on the number of participants. I'm thinking it'd be something like very small, small, medium, large and very large.
I could arbitrarily say something like:
* very small trial = less than 20 patients
* small = 21-99
* medium = 100-499
* large = 500-4999
* very large = 5000+
But, is there already some work in this area?
BW
jon
--
Jon Brassey
Trip Database
http://www.tripdatabase.com
Find evidence fast
------------------------------
Date: Wed, 5 Jun 2013 09:47:27 -0700
From: Paul Elias <[log in to unmask]>
Subject: Re: Categorising the size of a clinical trial
I have seen this in one study....
(<50 v small, 50-99 small,
100-199 low medium, 200-499 medium,
500-999 large, and ≥1000 patients very large).
Best,Paul E. Alexander
--- On Wed, 6/5/13, Dahm,Philipp <[log in to unmask]> wrote:
From: Dahm,Philipp <[log in to unmask]>
Subject: Re: Categorising the size of a clinical trial
To: [log in to unmask]
Received: Wednesday, June 5, 2013, 5:37 PM
Hello Jon:
I am curious – what is your purpose for categorizing trials by sample size?
Ph*
Philipp Dahm, MD, MHSc, FACS
Professor of Urology, University of Florida
Coordinating Editor, Cochrane Prostatic Diseases & Urological Cancers Group
College of Medicine, Health Science Center
Box 100247, Room N2-15
Gainesville, FL 32610-0247
Phone: (352) 273-8634
Fax: (352) 273-7515
Email: [log in to unmask]
From: Jon Brassey <[log in to unmask]>
Reply-To: Jon Brassey <[log in to unmask]>
Date: Wednesday, June 5, 2013 12:10 PM
To: Evidence health <[log in to unmask]>
Subject: Categorising the size of a clinical trial
Hi All,
This is a strange question, but would welcome any advice. I'm trying to create a system to categorise the size of trials, based on the number of participants. I'm thinking it'd be something like very small, small, medium, large and very large.
I could arbitrarily say something like:
very small trial = less than 20 patientssmall = 21-99medium = 100-499large = 500-4999very large = 5000+ But, is there already some work in this area?
BW
jon
--
Jon Brassey
Trip Database
http://www.tripdatabase.com
Find evidence fast
------------------------------
Date: Wed, 5 Jun 2013 16:53:32 +0000
From: "Johnson, E Diane" <[log in to unmask]>
Subject: Re: Categorising the size of a clinical trial
Hi Jon, FWIW, Embase has some index terms/check tags related to study size, although I'm not sure whether they are consistently applied:
Major clinical study: Original items reporting clinical work on greater than 50 patients Clinical article: Original items reporting clinical work on 5-50 patients Case Report: Original items reporting clinical work on not more than 4 individual cases
See p. 13 in the 2012 Embase indexing guide:
http://www.google.com/url?sa=t&rct=j&q=embase%20%22major%20clinical%20study%22&source=web&cd=1&cad=rja&ved=0CD4QFjAA&url=http%3A%2F%2Fcdn.elsevier.com%2Fassets%2Fpdf_file%2F0009%2F126873%2FEmbase-indexing-guide-2012.pdf&ei=2mqvUc_JCYaJrgGAiIGIBg&usg=AFQjCNEB2elhlum5L-NAu67EnTn2rpOUyg&bvm=bv.47380653,d.aWM
E. Diane Johnson
Assistant Director, Information Services and Resources J. Otto Lottes Health Sciences Library Univ of Missouri Columbia, MO 65212
573-882-6142
[log in to unmask]<mailto:[log in to unmask]>
Live Reference Available Weekdays from the Health Sciences Library Website!
http://healthlibrary.missouri.edu/contactus.cfm
From: Evidence based health (EBH) [mailto:[log in to unmask]] On Behalf Of Jon Brassey
Sent: Wednesday, June 05, 2013 11:11 AM
To: [log in to unmask]
Subject: Categorising the size of a clinical trial
Hi All,
This is a strange question, but would welcome any advice. I'm trying to create a system to categorise the size of trials, based on the number of participants. I'm thinking it'd be something like very small, small, medium, large and very large.
I could arbitrarily say something like:
* very small trial = less than 20 patients
* small = 21-99
* medium = 100-499
* large = 500-4999
* very large = 5000+
But, is there already some work in this area?
BW
jon
--
Jon Brassey
Trip Database
http://www.tripdatabase.com
Find evidence fast
------------------------------
Date: Wed, 5 Jun 2013 14:03:55 -0400
From: James Walker <[log in to unmask]>
Subject: Re: Categorising the size of a clinical trial
I'm wondering about the need for (and statistical wisdom of) translating a meaningful, computable value (the number of subjects) to a necessarily arbitrary set of categories--which users will have to remember how to translate back into an approximation of the original value.
Best regards.
On Jun 5, 2013, at 12:53 PM, "Johnson, E Diane" <[log in to unmask]> wrote:
> Hi Jon, FWIW, Embase has some index terms/check tags related to study size, although I’m not sure whether they are consistently applied:
>
> Major clinical study: Original items reporting clinical work on
> greater than 50 patients Clinical article: Original items reporting
> clinical work on 5-50 patients Case Report: Original items reporting
> clinical work on not more than 4 individual cases
>
> See p. 13 in the 2012 Embase indexing guide:
> http://www.google.com/url?sa=t&rct=j&q=embase%20%22major%20clinical%20
> study%22&source=web&cd=1&cad=rja&ved=0CD4QFjAA&url=http%3A%2F%2Fcdn.el
> sevier.com%2Fassets%2Fpdf_file%2F0009%2F126873%2FEmbase-indexing-guide
> -2012.pdf&ei=2mqvUc_JCYaJrgGAiIGIBg&usg=AFQjCNEB2elhlum5L-NAu67EnTn2rp
> OUyg&bvm=bv.47380653,d.aWM
>
>
>
> E. Diane Johnson
> Assistant Director, Information Services and Resources J. Otto Lottes
> Health Sciences Library Univ of Missouri Columbia, MO 65212
> 573-882-6142
> [log in to unmask]
>
> Live Reference Available Weekdays from the Health Sciences Library Website!
> http://healthlibrary.missouri.edu/contactus.cfm
>
>
>
>
> From: Evidence based health (EBH)
> [mailto:[log in to unmask]] On Behalf OfJon Brassey
> Sent: Wednesday, June 05, 2013 11:11 AM
> To: [log in to unmask]
> Subject: Categorising the size of a clinical trial
>
> Hi All,
>
> This is a strange question, but would welcome any advice. I'm trying to create a system to categorise the size of trials, based on the number of participants. I'm thinking it'd be something like very small, small, medium, large and very large.
>
> I could arbitrarily say something like:
>
> very small trial = less than 20 patients small = 21-99 medium =
> 100-499 large = 500-4999 very large = 5000+ But, is there already some
> work in this area?
>
> BW
>
> jon
>
> --
>
> Jon Brassey
> Trip Database
> http://www.tripdatabase.com
> Find evidence fast
>
------------------------------
Date: Wed, 5 Jun 2013 14:06:55 -0400
From: "Ansari, Mohammed" <[log in to unmask]>
Subject: Re: Categorising the size of a clinical trial
Other determinants of what defines a study size are - effect size, baseline risk/control event rates, and data dispersion. Size is relative to what magnitude is being measured under what conditions.
See this paper in JCE, issue 64, 2011
GRADE guidelines 6. Rating the quality of evidence -- imprecision
From: Evidence based health (EBH)
[mailto:[log in to unmask]] On Behalf Of James Walker
Sent: Wednesday, June 05, 2013 2:04 PM
To: [log in to unmask]
Subject: Re: Categorising the size of a clinical trial
I'm wondering about the need for (and statistical wisdom of) translating a meaningful, computable value (the number of subjects) to a necessarily arbitrary set of categories--which users will have to remember how to translate back into an approximation of the original value.
Best regards.
On Jun 5, 2013, at 12:53 PM, "Johnson, E Diane"
<[log in to unmask]> wrote:
Hi Jon, FWIW, Embase has some index terms/check tags related to study size, although I'm not sure whether they are consistently applied:
Major clinical study: Original items reporting clinical work on greater than 50 patients
Clinical article: Original items reporting clinical work on 5-50 patients
Case Report: Original items reporting clinical work on not more than 4 individual cases
See p. 13 in the 2012 Embase indexing guide:
http://www.google.com/url?sa=t&rct=j&q=embase%20%22major%20clinical%20st
udy%22&source=web&cd=1&cad=rja&ved=0CD4QFjAA&url=http%3A%2F%2Fcdn.elsevi
er.com%2Fassets%2Fpdf_file%2F0009%2F126873%2FEmbase-indexing-guide-2012.
pdf&ei=2mqvUc_JCYaJrgGAiIGIBg&usg=AFQjCNEB2elhlum5L-NAu67EnTn2rpOUyg&bvm
=bv.47380653,d.aWM
<http://www.google.com/url?sa=t&rct=j&q=embase%20%22major%20clinical%20s
tudy%22&source=web&cd=1&cad=rja&ved=0CD4QFjAA&url=http%3A%2F%2Fcdn.elsev
ier.com%2Fassets%2Fpdf_file%2F0009%2F126873%2FEmbase-indexing-guide-2012
.pdf&ei=2mqvUc_JCYaJrgGAiIGIBg&usg=AFQjCNEB2elhlum5L-NAu67EnTn2rpOUyg&bv
m=bv.47380653,d.aWM>
E. Diane Johnson
Assistant Director, Information Services and Resources
J. Otto Lottes Health Sciences Library
Univ of Missouri
Columbia, MO 65212
573-882-6142
[log in to unmask] <mailto:[log in to unmask]>
Live Reference Available Weekdays from the Health Sciences Library Website!
http://healthlibrary.missouri.edu/contactus.cfm
<http://healthlibrary.missouri.edu/contactus.cfm>
From: Evidence based health (EBH)
[mailto:[log in to unmask]] On Behalf OfJon Brassey
Sent: Wednesday, June 05, 2013 11:11 AM
To: [log in to unmask]
Subject: Categorising the size of a clinical trial
Hi All,
This is a strange question, but would welcome any advice. I'm trying to create a system to categorise the size of trials, based on the number of participants. I'm thinking it'd be something like very small, small, medium, large and very large.
I could arbitrarily say something like:
* very small trial = less than 20 patients
* small = 21-99
* medium = 100-499
* large = 500-4999
* very large = 5000+
But, is there already some work in this area?
BW
jon
--
Jon Brassey
Trip Database
http://www.tripdatabase.com <http://www.tripdatabase.com>
Find evidence fast
--------------------
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--------------------
------------------------------
Date: Wed, 5 Jun 2013 21:38:26 +0330
From: Farhad Shokraneh <[log in to unmask]>
Subject: Re: Categorising the size of a clinical trial
Dear Jon,
I think the terms small and large might not be same for all disease. For instance a clinical trial including 20 patients with a rare condition/disease still is large. Despite this, I suggest *Phases *(encompassing the terms large/small) of clinical trials as used in PubMed (Article Types) or clinicaltrials <http://www.nlm.nih.gov/services/ctphases.html>. Also, Wikipedia <http://en.wikipedia.org/wiki/Clinical_trial#Phases> has mentioned number of participants in each phase but I couldn't find its Reference.
I have the as same question as Philipp's. Is this about new upgrades of TRIP?
Bests,
Farhad
On Wed, Jun 5, 2013 at 7:40 PM, Jon Brassey <[log in to unmask]>wrote:
> Hi All,
>
> This is a strange question, but would welcome any advice. I'm trying
> to create a system to categorise the size of trials, based on the
> number of participants. I'm thinking it'd be something like very
> small, small, medium, large and very large.
>
> I could arbitrarily say something like:
>
>
> - very small trial = less than 20 patients
> - small = 21-99
> - medium = 100-499
> - large = 500-4999
> - very large = 5000+
>
> But, is there already some work in this area?
>
> BW
>
> jon
>
> --
>
> Jon Brassey
> Trip Database
> http://www.tripdatabase.com
> Find evidence fast
>
>
--
*Farhad Shokraneh*, BSc, MS, MedLIS
Iranian Center for Evidence-Based Medicine, Tabriz University of Medical Sciences, Tabriz, Iran Cell Phone: +98 (0) 9149567734 Google Scholar Profile<http://scholar.google.com/citations?hl=en&user=bpljzVEAAAAJ&view_op=list_works&pagesize=100>
ResearchGate Profile<https://www.researchgate.net/profile/Farhad_Shokraneh/>
------------------------------
Date: Wed, 5 Jun 2013 20:17:27 +0200
From: Tom Jefferson <[log in to unmask]>
Subject: Re: Categorising the size of a clinical trial
Very interesting discussion. As Mohammed suggest, it revolves around what you mean by size.
If it's denominator, which denominator?
And: according to the publication or the CSR? (That is if you know there have been one or more trials of course)
Thank you, guys: very stimulating.
Tom.
On 5 June 2013 20:08, Farhad Shokraneh <[log in to unmask]> wrote:
> Dear Jon,
>
> I think the terms small and large might not be same for all disease.
> For instance a clinical trial including 20 patients with a rare
> condition/disease still is large. Despite this, I suggest *Phases
> *(encompassing the terms large/small) of clinical trials as used in
> PubMed (Article Types) or clinicaltrials
> <http://www.nlm.nih.gov/services/ctphases.html>. Also, Wikipedia
> <http://en.wikipedia.org/wiki/Clinical_trial#Phases> has mentioned
> number of participants in each phase but I couldn't find its Reference.
>
> I have the as same question as Philipp's. Is this about new upgrades
> of TRIP?
>
> Bests,
> Farhad
>
>
>
> On Wed, Jun 5, 2013 at 7:40 PM, Jon Brassey <[log in to unmask]>wrote:
>
>> Hi All,
>>
>> This is a strange question, but would welcome any advice. I'm trying
>> to create a system to categorise the size of trials, based on the
>> number of participants. I'm thinking it'd be something like very
>> small, small, medium, large and very large.
>>
>> I could arbitrarily say something like:
>>
>>
>> - very small trial = less than 20 patients
>> - small = 21-99
>> - medium = 100-499
>> - large = 500-4999
>> - very large = 5000+
>>
>> But, is there already some work in this area?
>>
>> BW
>>
>> jon
>>
>> --
>>
>> Jon Brassey
>> Trip Database
>> http://www.tripdatabase.com
>> Find evidence fast
>>
>>
>
>
>
> --
> *Farhad Shokraneh*, BSc, MS, MedLIS
>
> Iranian Center for Evidence-Based Medicine, Tabriz University of
> Medical Sciences, Tabriz, Iran Cell Phone: +98 (0) 9149567734 Google
> Scholar
> Profile<http://scholar.google.com/citations?hl=en&user=bpljzVEAAAAJ&vi
> ew_op=list_works&pagesize=100> ResearchGate
> Profile<https://www.researchgate.net/profile/Farhad_Shokraneh/>
>
--
Dr Tom Jefferson
Medico Chirurgo
GMC # 2527527
www.attentiallebufale.it
------------------------------
Date: Wed, 5 Jun 2013 20:12:18 +0000
From: Juan Acuna <[log in to unmask]>
Subject: Re: Categorising the size of a clinical trial
Hi all,
Interesting discussion. Thanks for sharing.
I think two issues are being mixed here:
1. The "absolute" size of the trial (number of subjects).
2. The sample size.
Several comments addressed the first one and I see of not a dramatic importance to classify a study (whether a trial or not) according to its size, unless such classification is required for specific purposes (such as database classification, etc.).
Of more relevance and importance is that the size of the sample is probably related to both the internal and external validity of a given study thus, related to the quality of the study.
Sample size (SS) is determined (simplistically speaking) by the level of significance set for the study (the size of the random error that we need to account for, and the numerator of the SS formula) and the size of the effect that the study wants to detect (and in essence, the denominator in the SS formula). The consequence of considering these elements in the context on the absolute size (number of subjects in the study) is that given the right conditions, a small SS could be appropriate. In other words, and relevant to the SS, a small study could be a good and valid study. In inadequate conditions, even a large sample size could threaten the internal validity (and external validity) of a study. In other simpler words, a large study could be a bad study.
Conclusion: absolute size of a study and quality (as it relates to the SS) are neither equivalent nor always related.
I hope this helps.
JA
Juan M. Acuña M.D., MSc., FACOG.
FIU Assistant Vice-President for Clinical and Community Research Associate Professor of Human and Molecular Genetics and Clinical Epidemiology, FIU Herbert Wertheim College of Medicine
Director, Division of Research and Information And Data Coordinating Center Florida International University Herbert Wertheim College of Medicine
Guest Researcher, Division of Reproductive Health Centers for Disease Control and Prevention
11200 SW 8th Street
AHC2-474
Miami, FL 33199
Ph (305) 348-0676
From: Evidence based health (EBH) [mailto:[log in to unmask]] On Behalf Of Farhad Shokraneh
Sent: Wednesday, June 05, 2013 2:08 PM
To: [log in to unmask]
Subject: Re: Categorising the size of a clinical trial
Dear Jon,
I think the terms small and large might not be same for all disease. For instance a clinical trial including 20 patients with a rare condition/disease still is large. Despite this, I suggest Phases (encompassing the terms large/small) of clinical trials as used in PubMed (Article Types) or clinicaltrials<http://www.nlm.nih.gov/services/ctphases.html>. Also, Wikipedia<http://en.wikipedia.org/wiki/Clinical_trial#Phases> has mentioned number of participants in each phase but I couldn't find its Reference.
I have the as same question as Philipp's. Is this about new upgrades of TRIP?
Bests,
Farhad
On Wed, Jun 5, 2013 at 7:40 PM, Jon Brassey <[log in to unmask]<mailto:[log in to unmask]>> wrote:
Hi All,
This is a strange question, but would welcome any advice. I'm trying to create a system to categorise the size of trials, based on the number of participants. I'm thinking it'd be something like very small, small, medium, large and very large.
I could arbitrarily say something like:
* very small trial = less than 20 patients
* small = 21-99
* medium = 100-499
* large = 500-4999
* very large = 5000+
But, is there already some work in this area?
BW
jon
--
Jon Brassey
Trip Database
http://www.tripdatabase.com
Find evidence fast
--
Farhad Shokraneh, BSc, MS, MedLIS
Iranian Center for Evidence-Based Medicine, Tabriz University of Medical Sciences, Tabriz, Iran Cell Phone: +98 (0) 9149567734 Google Scholar Profile<http://scholar.google.com/citations?hl=en&user=bpljzVEAAAAJ&view_op=list_works&pagesize=100>
ResearchGate Profile<https://www.researchgate.net/profile/Farhad_Shokraneh/>
------------------------------
Date: Wed, 5 Jun 2013 21:28:13 +0000
From: "Yao, Xiaomei" <[log in to unmask]>
Subject: Re: Categorising the size of a clinical trial
[Message contains invalid MIME fields or encoding and could not be processed]
------------------------------
End of EVIDENCE-BASED-HEALTH Digest - 4 Jun 2013 to 5 Jun 2013 (#2013-141)
**************************************************************************
