A report of a randomised controlled trial (RCT) should
convey to the reader, in a transparent manner, why the
study was undertaken, and how it was conducted and
analysed. Inadequately reported randomisation, for
example, has been associated with bias in estimating the
effectiveness of interventions.
1,2
To assess the strengths and
limitations of an RCT, readers need and deserve to know
the quality of its methods.
Despite several decades of educational efforts, RCTs are
still not being reported adequately.
3–6
For example, a
review
5
of 122 recently published RCTs that assessed the
effectiveness of selective serotonin reuptake inhibitors as a
first-line management strategy for depression found that
only one paper described randomisation adequately.
Inadequate reporting makes the interpretation of RCTs
difficult, if not impossible. Moreover, inadequate reporting
borders on unethical practice when biased results receive
false credibility.
History of CONSORT
In the mid-1990s, two independent initiatives to improve
the quality of reports of RCTs led to the publication of the
CONSORT statement,
7
which was developed by an
Lancet 2001; 357: 1191–94
*Members listed at end of paper
The revised CONSORT statement is also published in JAMA 2001;
285: 1987–91 and Ann Intern Med 2001; 134: 657–62.
University of Ottawa, Thomas C Chalmers Centre for Systematic
Reviews, Ottawa, Ontario, Canada (D Moher
MSc); Family Health
International and Department of Obstetrics and Gynecology,
School of Medicine, University of North Carolina at Chapel Hill, NC,
USA (K F Schulz
PhD); and ICRF Medical Statistics Group and
Centre for Statistics in Medicine, Institute of Health Sciences,
Oxford, UK (D G Altman
DSc)
Correspondence to: Dr Leah Lepage, Thomas C Chalmers Centre for
Systematic Reviews, Children’s Hospital of Eastern Ontario Research
Institute, Room R235, 401 Smyth Road, Ottawa, Ontario K1H 8L1,
Canada
(e-mail: llepage@uottawa.ca)
international group of clinical trialists, statisticians,
epidemiologists, and biomedical editors. CONSORT has
been supported by a growing number of medical and
health-care journals
8–11
and editorial groups, including the
International Committee of Medical Journal Editors
(ICMJE, The Vancouver Group),
12
the Council of Science
Editors (CSE), and the World Association of Medical
Editors (WAME). CONSORT is published in Dutch,
English, French, German, Japanese, and Spanish. It can be
accessed together with other information about the
CONSORT group on the internet.
13
The CONSORT statement consists of a checklist and
flow diagram for reporting an RCT. For convenience, the
checklist and diagram together are called simply
CONSORT. They are primarily intended for use in
writing, reviewing, or assessing reports of simple two-group
parallel RCTs.
Preliminary data indicate that the use of CONSORT
does indeed help to improve the quality of reports of
RCTs.
14,15
In an assessment
14
of 71 RCTs, published in
three journals in 1994, allocation concealment was not
clearly reported in 43 (61%) of the trials. 4 years later, after
these three journals required that authors reporting an
RCT use CONSORT, the proportion of papers in which
allocation concealment was not clearly reported had
dropped to 30 of 77 (39%, mean difference ⫺22% [95%
CI ⫺38 to ⫺6]).
The usefulness of CONSORT is increased by
continuous monitoring of biomedical publications, which
allows it to be modified dependent on the merits of
maintaining or dropping current items, and including new
items. For example, when Meinert
16
observed that the flow
diagram did not provide important information about the
number of participants who entered each phase of an RCT
(ie, enrolment, treatment allocation, follow-up, and data
analysis), the diagram could be modified to accommodate
the information. The checklist is similarly flexible.
This iterative process makes the CONSORT statement a
continually evolving instrument. Although participants in
the CONSORT group and their degree of involvement vary
over time, members meet regularly to review the need to
The CONSORT statement: revised recommendations for improving
the quality of reports of parallel-group randomised trials
David Moher, Kenneth F Schulz, Douglas G Altman, for the CONSORT Group*
To comprehend the results of a randomised controlled trial (RCT), readers must understand its design, conduct, analysis,
and interpretation. That goal can be achieved only through total transparency from authors. Despite several decades of
educational efforts, the reporting of RCTs needs improvement. Investigators and editors developed the original CONSORT
(Consolidated Standards of Reporting Trials) statement to help authors improve reporting by use of a checklist and flow
diagram. The revised CONSORT statement presented here incorporates new evidence and addresses some criticisms of
the original statement. The checklist items pertain to the content of the Title, Abstract, Introduction, Methods, Results,
and Discussion. The revised checklist includes 22 items selected because empirical evidence indicates that not reporting
this information is associated with biased estimates of treatment effect, or because the information is essential to judge
the reliability or relevance of the findings. We intended the flow diagram to depict the passage of participants through an
RCT. The revised flow diagram depicts information from four stages of a trial (enrolment, intervention allocation, follow-
up, and analysis). The diagram explicitly shows the number of participants, for each intervention group, included in the
primary data analysis. Inclusion of these numbers allows the reader to judge whether the authors have done an intention-
to-treat analysis. In sum, the CONSORT statement is intended to improve the reporting of an RCT, enabling readers to
understand a trial’s conduct and to assess the validity of its results.
refine CONSORT. At the 1999 meeting, the participants
decided to revise the original statement. This report reflects
changes determined by consensus of the CONSORT
group, partly in response to emerging evidence on the
importance of various elements of RCTs.
Revision of the CONSORT statement
13 members of the CONSORT group met in May, 1999,
with the main objective of revising the original CONSORT
checklist and flow diagram, as needed. The group discussed
the merits of including each item in the light of current
evidence. As in developing the original CONSORT
statement, our intention was to keep only those items
deemed fundamental to reporting standards for an RCT.
Some items not regarded as essential could well be highly
desirable and should still be included in an RCT report
even though they are not included in CONSORT. Such
items include approval of an institutional ethics review
board, sources of funding for the trial, and a trial registry
number—eg, the International Standard Randomized
Controlled Trial Number (ISRCTN) used to register the
RCT at its inception.
17
Shortly after the meeting, a revised version of the
checklist was circulated to the group for additional
comments and feedback. Revisions to the flow diagram
were similarly made. All these changes were discussed when
CONSORT participants met in May, 2000, and the revised
statement was finalised shortly afterwards.
The revised CONSORT statement includes a 22-item
checklist (table) and a flow diagram (figure). Its main aim is
to help authors improve the quality of reports of simple
two-group parallel RCTs. However, the basic philosophy
underlying the development of the statement can be applied
to any design. In this respect, additional statements for
other designs will be forthcoming from the group.
CONSORT can also be used by peer reviewers and editors
to identify reports with inadequate description of trials and
those with potentially biased results.
1,2
During the 1999 meeting, the group also discussed the
benefits of developing an explanatory document to improve
the use and dissemination of CONSORT. The document is
patterned on reporting of statistical aspects of clinical
research,
18
and was developed to help facilitate the
recommendations of the ICMJE’s Uniform Requirements
for Manuscripts Submitted to Biomedical Journals. Three
members of the CONSORT group, with assistance from
members on some checklist items, drafted an explanation
and elaboration document. That document
19
was circulated
to the group for additions and revisions and was last revised
after review at the latest CONSORT group meeting.
Changes to CONSORT
(1) In the revised checklist, a new column for “Paper
section and topic” integrates information from the
“Subheading” column that was contained in the original
statement.
(2) The “Was it reported?” column has been integrated
into a “reported on page number” column, as requested by
some journals.
(3) Each item of the checklist is now numbered and the
syntax and order have been revised to improve the flow of
information.
(4) “Title” and “Abstract” are now combined in the first
item.
(5) Although the content of the revised checklist is similar
to the original, some items that were previously combined
Item Descriptor Reported on
number page number
Title and abstract 1 How participants were allocated to interventions (eg, “random allocation”, “randomised”, or “randomly assigned”).
Introduction
Background 2 Scientified background and explanation of rationale.
Methods
Participants 3 Eligibility criteria for participants and the settings and locations where the data were collected.
Interventions 4 Precise details of the interventions intended for each group and how and when they were actually administered.
Objectives 5 Specific objectives and hypotheses.
Outcomes 6 Clearly defined primary and secondary outcome measures and, when applicable, any methods used to enhance the quality of
measurements (eg, multiple observations, training of assessors, &c).
Sample size 7 How sample size was determined and, when applicable, explanation of any interim analyses and stopping rules.
Randomisation
Sequence generation 8 Method used to generate the random allocation sequence, including details of any restriction (eg, blocking, stratification).
Allocation concealment 9 Method used to implement the random allocation sequence (eg, numbered containers or central telephone), clarifying
whether the sequence was concealed until interventions were assigned.
Implementation 10 Who generated the allocation sequence, who enrolled participants, and who assigned participants to their groups.
Blinding (masking) 11 Whether or not participants, those administering the interventions, and those assessing the outcomes were aware of group
assignment. If not, how the success of masking was assessed.
Statistical methods 12 Statistical methods used to compare groups for primary outcome(s); methods for additional analyses, such as subgroup
analyses and adjusted analyses.
Results
Participant flow 13 Flow of participants through each stage (a diagram is strongly recommended). Specifically, for each group, report the numbers
of participants randomly assigned, receiving intended treatment, completing the study protocol, and analysed for the primary
outcome. Describe protocol deviations from study as planned, together with reasons.
Recruitment 14 Dates defining the periods of recruitment and follow-up.
Baseline data 15 Baseline demographic and clinical characteristics of each group.
Numbers analysed 16 Number of participants (denominator) in each group included in each analysis and whether the analysis was by “intention to
treat”. State the results in absolute numbers when feasible (eg, 10/20, not 50%).
Outcomes and estimation 17 For each primary and secondary outcome, a summary of results for each group, and the estimated effect size and its
precision (eg, 95% CI).
Ancillary analyses 18 Address multiplicity by reporting any other analyses performed, including subgroup analyses and adjusted analyses,
indicating those prespecified and those exploratory.
Adverse events 19 All important adverse events or side-effects in each intervention group.
Discussion
Interpretation 20 Interpretation of the results, taking into account study hypotheses, sources of potential bias or imprecision and the dangers
associated with multiplicity of analyses and outcomes.
Generalisability 21 Generalisability (external validity) of the trial findings.
Overall evidence 22 General interpretation of the results in the context of current evidence.
Checklist of items to include when reporting a randomised trial
are now separate. For example, previously authors were
asked to describe “primary and secondary outcome(s)
measure(s) and the minimum important difference(s), and
indicate how the target sample size was projected”. In the
new version, issues pertaining to outcomes (item 6) and
sample size (item 7) are separate, enabling authors to be
more explicit about each. Moreover, some items request
additional information. For example, for outcomes, authors
are asked to report any methods used to improve the quality
of measurements, such as multiple observations.
(6) The item asking for the unit of randomisation (eg,
cluster) has been dropped because specific checklists have
been developed for reporting cluster RCTs
20
and other
design types
13
since publication of the original checklist.
(7) Whenever possible, new evidence is incorporated into
the revised checklist. For example, authors are asked to be
explicit about whether the analysis reported is by intention
to treat (item 16). This request is based partly on the
observations
21
that authors do not adequately describe and
apply intention-to-treat analysis, and that reports not
providing this information are less likely to provide other
relevant information such as losses to follow-up.
22
(8)The revised flow diagram depicts information from four
stages of a trial (enrolment, intervention allocation, follow-
up, and analysis). The revised diagram explicitly shows the
number of participants, for each intervention group,
included in the primary data analysis. Inclusion of these
numbers lets the reader know whether the authors have
done an intention-to-treat analysis.
21–23
Because some of the
information might not always be known, and to
accommodate other information, the structure of the flow
diagram might need to be modified for a particular trial.
Inclusion of the participant flow diagram in the report is
strongly recommended but might be unnecessary for simple
trials such as those without any participant withdrawals or
dropouts.
Discussion
Specifically developed to guide authors about how to
improve the quality of reporting of simple two-group
parallel RCTs, CONSORT encourages transparency with
reporting of the methods and results so that reports of
RCTs can be interpreted readily and accurately. However,
CONSORT does not address other facets of reporting that
also require attention, such as scientific content and
readability of RCT reports. Some authors in their
enthusiasm to use CONSORT have modified the
checklist.
24
We recommend against such modifications
because they could be based on a different process from the
one used by the CONSORT group.
The use of CONSORT seems to reduce, if not eliminate,
inadequate reporting of RCTs.
14,15
Potentially, the use of
CONSORT should positively influence the manner in
which RCTs are conducted. Granting agencies have noted
this potential relation, and in at least one case
25
have
encouraged researchers to consider in their application how
they have dealt with the CONSORT items.
The evidence-based approach used to develop
CONSORT has also been used to develop standards for
reporting meta-analyses of randomised trials,
26
meta-
analyses of observational studies,
27
and diagnostic studies
(Jeroen Lijmer, personal communication). Health
economists have also started to develop reporting
standards
28
to help to improve the quality of their reports.
29
The intent of all these initiatives is to improve the quality of
reporting of biomedical research,
30
and by doing so, to bring
about more effective health care.
The revised CONSORT statement will replace the
original one in the journals and groups that already support
it. Journals that do not yet support CONSORT may do so
by registering on the CONSORT website.
13
To convey to
authors the importance of improved quality in the reporting
of RCTs, we encourage supporting journals to reference the
revised CONSORT statement and the CONSORT
internet address in their Instructions to Contributors. Since
the journals publishing the revised CONSORT statement
have waived copyright protection, CONSORT is now
widely accessible to the biomedical community. The
CONSORT checklist and flow diagram can also be
accessed at the CONSORT website.
A lack of clarification of the meaning and rationale for
each checklist item in the original CONSORT statement
has been remedied with the development of the
CONSORT explanation and elaboration document,
19
which can also be found on the CONSORT website. This
document reports the evidence on which the checklist items
are based, including the references, which had annotated
the checklist items in the previous version. We also
Randomised (n=...)
Assessed for
eligibility (n=...)
Excluded (n=...)
Not meeting
inclusion
criteria (n=...)
Refused to
participate (n=...)
Other reasons
(n=...)
Allocated to
intervention (n=...)
Received allocated
intervention (n=...)
Did not receive
allocated
intervention;
give reasons (n=...)
Lost to follow-up;
give reasons (n=...)
Discontinued
intervention;
give reasons (n=...)
Analysed (n=...)
Excluded from
analysis;
give reasons (n=...)
Allocated to
intervention (n=...)
Received allocated
intervention (n=...)
Did not receive
allocated
intervention;
give reasons (n=...)
Lost to follow-up;
give reasons (n=...)
Discontinued
intervention;
give reasons (n=...)
Analysed (n=...)
Excluded from
analysis;
give reasons (n=...)
Analysis
Follow-up
Allocation
Enrolment
Flow diagram of the progress through the phases of a
randomised trial
encourage journals to include reference to this document in
their Instructions to Contributors.
Emphasising the evolving nature of CONSORT, the
CONSORT group invites readers to comment on the
updated checklist and flow diagram through the
CONSORT website.
13
Comments and suggestions will be
collated and considered at the next meeting of the group in
2001.
Contributors
David Moher, Ken Schulz, and Doug Altman participated in regular
conference calls, identified participants, participated in the CONSORT
meetings, and drafted the paper. David Moher and Leah Lepage planned
the CONSORT meetings, identified and secured funding, invited the
participants, and planned the meeting agenda. The members of the
CONSORT group listed below attended the CONSORT meetings and
provided input towards the revised checklist, flow diagram, and text.
The CONSORT group
Frank Davidoff (Annals of Internal Medicine, Philadelphia, PA, USA);
Susan Eastwood (University of California at San Francisco, CA, USA);
Matthias Egger (Department of Social Medicine, University of Bristol,
UK); Diana Elbourne (London School of Hygiene and Tropical Medicine,
London, UK); Peter Gøtzsche (Nordic Cochrane Centre, Copenhagen,
Denmark); Sylvan B Green (School of Medicine, Case Western Reserve
University, Cleveland, OH, USA); Leni Grossman (Merck & Co,
Whitehouse Station, NJ, USA); Barbara S Hawkins (Wilmer Ophthal-
mological Institute, Johns Hopkins University, (Baltimore, MD, USA);
Richard Horton (The Lancet, London, UK); Wayne B Jonas (Uniformed
Services University of the Health Sciences, Bethesda, MD); Terry Klassen
(Department of Pediatrics, University of Alberta, Edmonton, Alberta,
Canada); Leah Lepage (Thomas C Chalmers Centre for Systematic
Reviews, Ottawa, Ontario, Canada); Thomas Lang (Tom Lang
Communications, Lakewood, OH, USA); Jeroen Lijmer (Department of
Clinical Epidemiology, University of Amsterdam, Netherlands);
Rick Malone (TAP Pharmaceuticals, Lake Forest, IL, USA);
Curtis L Meinert (Johns Hopkins University, Baltimore, MD);
Mary Mosley (Life Science Publishing, Tokyo, Japan); Stuart Pocock
(London School of Hygiene and Tropical Medicine, London); Drummond
Rennie (Journal of the American Medical Association, Chicago, IL);
David S Riley (University of New Mexico Medical School, Santa Fe, NM,
USA); Roberta W Scherer (Epidemiology & Preventive Medicine,
University of Maryland School of Medicine, Baltimore, MD); Ida Sim
(University of California at San Francisco, CA); Donna Stroup
(Epidemiology Program Office, Centers for Disease Control and
Prevention, Atlanta, GA, USA).
Acknowledgments
The effort to improve the reporting of randomised trials, from its beginnings
with the Standards of Reporting Trials (SORT) group to the current
activities of the Consolidated Standards of Reporting Trials (CONSORT)
group, has involved many people around the globe. We thank Leah Lepage
for keeping everybody all lined up and moving in the same direction.
Financial support to convene meetings of the CONSORT group was
provided in part by Abbott Laboratories, American College of Physicians,
GlaxoWellcome, The Lancet, Merck, the Canadian Institutes for Health
Research, National Library of Medicine, and TAP Pharmaceuticals.
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