Mr. Schwarz brings up the idea of a "single-blind" study as one in
which EITHER the human subject(s) or the experimenter(s) making the
clinical measurements are unaware of the trial conditions at the time of
measurement.
If indeed this was the meaning intended both in the criticized diet
study and the criticism of it, then the term may not have been misused by
Al-Marzouki et al, depending on which meaning was intended in the diet
study.
But, this raises other questions: If the subjects know the
conditions, why blind the experimenters? What use could this serve? The
experimenters merely could ask the subjects during the trials some
question revealing the group assigned. "How have you been feeling since
going on the fruit diet? Step onto the scale." If Mr. Schwarz's
definition was intended, then unblinded bias again would be as likely as
fraud as an explanation of some of the bias found in the statistical
averages.
Measurements of weight or heart rate are objective, so the Schwarz
use of "single-blind" would seem intended primarily to prevent intentional
falsification rather than unconscious bias. But, as just pointed out, an
INTENTION to fabricate would sidestep this kind of "single-blind" easily.
If this is a real difference in usage, it might be worthwhile for BMJ
or its interested readers to try to come to agreement on terminology on
this issue. Mr. Schwarz cites no reference for his definition of "single
-blind"; but, it would have been useful to be able to examine this
question in more detail.
It would appear that the usage proposed by Mr. Schwarz is ambiguous
and thus liable to be misused. What about a diet study in which the food
looks the same to the subjects, or an exercise study in which the subjects
can tell what they are doing, but do not know otherwise the purpose of the
study? This reverses the meaning of "single-blind" (experimenter vs.
subject) with no hint of this reversal to the reader.
I tried a search for "Single Blind" on Yahoo and on Google. Only one
of the first few dozen pages returned agreed with Mr. Schwarz's definition
(http://www.medterms.com). The NCI and other sites, which could be
considered authoritative, all unequivocally define "single-blind" the way
it is used in the reference I cited previously. Unfortunately, my old
copy of the Merck Manual does not address experimentation of this kind.
It is unclear to me whether Mr. Schwarz should have referred to his
definition as "scientific". It would be useful to know the context in
which Mr. Schwarz's definition has been used in science, and by whom
(other than the apparently erroneous usage by Al-Marzouki et al pointed
out in my previous posting).
Competing interests:
None declared
Competing interests:
No competing interests
11 August 2005
John M. Williams
business owner
Markanix Co., P. O. Box 2697, Redwood City, CA 94064
Rapid Response:
Single Blind is Double Blind, Revisited
Mr. Schwarz brings up the idea of a "single-blind" study as one in
which EITHER the human subject(s) or the experimenter(s) making the
clinical measurements are unaware of the trial conditions at the time of
measurement.
If indeed this was the meaning intended both in the criticized diet
study and the criticism of it, then the term may not have been misused by
Al-Marzouki et al, depending on which meaning was intended in the diet
study.
But, this raises other questions: If the subjects know the
conditions, why blind the experimenters? What use could this serve? The
experimenters merely could ask the subjects during the trials some
question revealing the group assigned. "How have you been feeling since
going on the fruit diet? Step onto the scale." If Mr. Schwarz's
definition was intended, then unblinded bias again would be as likely as
fraud as an explanation of some of the bias found in the statistical
averages.
Measurements of weight or heart rate are objective, so the Schwarz
use of "single-blind" would seem intended primarily to prevent intentional
falsification rather than unconscious bias. But, as just pointed out, an
INTENTION to fabricate would sidestep this kind of "single-blind" easily.
If this is a real difference in usage, it might be worthwhile for BMJ
or its interested readers to try to come to agreement on terminology on
this issue. Mr. Schwarz cites no reference for his definition of "single
-blind"; but, it would have been useful to be able to examine this
question in more detail.
It would appear that the usage proposed by Mr. Schwarz is ambiguous
and thus liable to be misused. What about a diet study in which the food
looks the same to the subjects, or an exercise study in which the subjects
can tell what they are doing, but do not know otherwise the purpose of the
study? This reverses the meaning of "single-blind" (experimenter vs.
subject) with no hint of this reversal to the reader.
I tried a search for "Single Blind" on Yahoo and on Google. Only one
of the first few dozen pages returned agreed with Mr. Schwarz's definition
(http://www.medterms.com). The NCI and other sites, which could be
considered authoritative, all unequivocally define "single-blind" the way
it is used in the reference I cited previously. Unfortunately, my old
copy of the Merck Manual does not address experimentation of this kind.
It is unclear to me whether Mr. Schwarz should have referred to his
definition as "scientific". It would be useful to know the context in
which Mr. Schwarz's definition has been used in science, and by whom
(other than the apparently erroneous usage by Al-Marzouki et al pointed
out in my previous posting).
Competing interests:
None declared
Competing interests: No competing interests