There is no official definition of many terms used in randomised
trials, including double blind, single blind, intention to treat, and so
on. The term randomised does have precise technical meaning but it is
often misused. Labels are valuable only if they have a unique meaning and
are only used in the correct way.
John Williams queries the definition of a single blind trial. One
publication in the BMJ states that in a single blind trial “either only
the investigator or only the patient is blind to the allocation”.[1] The
term is thus unhelpful without clarification. Double blind trials are
just as confusing as single blind trials. A survey of physicians and a
review of textbooks and reports revealed numerous interpretations of the
designation “double-blind.”[2] Of key importance in both single and
double blind trials is whether the outcome assessor is blinded.
Hence the CONSORT Statement avoids labels and asks for specific
information: “Whether or not participants, those administering the
interventions, and those assessing the outcomes were blinded to group
assignment. If done, how the success of blinding was evaluated.”[3]
Likewise, in an article in which we tried to clarify the various
“terminological tangles” associated with blinding, we wrote: “we urge that
authors explicitly state what steps were taken to keep whom blinded. If
they choose to use terminology such as single-, double-, or triple-
blinding in reporting randomized controlled trials, they should explicitly
define those terms.”[4]
Arguments about the correct meaning of “single-blind” are pointless.
1 Day SJ, Altman DG. Blinding in clinical trials and other studies.
BMJ 2000;321:504.
2 Devereaux PJ, Manns BJ, Ghali WA, Quan H, Lacchetti C, Montori VM,
et al. Physician interpretations and textbook definitions of blinding
terminology in randomized controlled trials. JAMA 2001;285:2000-3.
3 Moher D, Schulz KF, Altman D for the CONSORT Group. The CONSORT
statement: revised recommendations for improving the quality of reports of
parallel-group randomized trials. JAMA 2001;285:1987-91. [see also www.consort-statement.com]
4 Schulz KF, Chalmers I, Altman DG. The landscape and lexicon of
blinding in randomized trials. Ann Intern Med 2002;136:254-9.
Rapid Response:
What is a single blind trial?
There is no official definition of many terms used in randomised
trials, including double blind, single blind, intention to treat, and so
on. The term randomised does have precise technical meaning but it is
often misused. Labels are valuable only if they have a unique meaning and
are only used in the correct way.
John Williams queries the definition of a single blind trial. One
publication in the BMJ states that in a single blind trial “either only
the investigator or only the patient is blind to the allocation”.[1] The
term is thus unhelpful without clarification. Double blind trials are
just as confusing as single blind trials. A survey of physicians and a
review of textbooks and reports revealed numerous interpretations of the
designation “double-blind.”[2] Of key importance in both single and
double blind trials is whether the outcome assessor is blinded.
Hence the CONSORT Statement avoids labels and asks for specific
information: “Whether or not participants, those administering the
interventions, and those assessing the outcomes were blinded to group
assignment. If done, how the success of blinding was evaluated.”[3]
Likewise, in an article in which we tried to clarify the various
“terminological tangles” associated with blinding, we wrote: “we urge that
authors explicitly state what steps were taken to keep whom blinded. If
they choose to use terminology such as single-, double-, or triple-
blinding in reporting randomized controlled trials, they should explicitly
define those terms.”[4]
Arguments about the correct meaning of “single-blind” are pointless.
1 Day SJ, Altman DG. Blinding in clinical trials and other studies.
BMJ 2000;321:504.
2 Devereaux PJ, Manns BJ, Ghali WA, Quan H, Lacchetti C, Montori VM,
et al. Physician interpretations and textbook definitions of blinding
terminology in randomized controlled trials. JAMA 2001;285:2000-3.
3 Moher D, Schulz KF, Altman D for the CONSORT Group. The CONSORT
statement: revised recommendations for improving the quality of reports of
parallel-group randomized trials. JAMA 2001;285:1987-91. [see also
www.consort-statement.com]
4 Schulz KF, Chalmers I, Altman DG. The landscape and lexicon of
blinding in randomized trials. Ann Intern Med 2002;136:254-9.
Competing interests:
None declared
Competing interests: No competing interests