Author Affiliations: Department of Family and Community Medicine, University of California, Davis.
Context Ongoing efforts to improve the quality of reporting for randomized controlled
trials (RCTs) include the Consolidated Standards of Reporting Trials (CONSORT)
statement. We examined the frequency of explicit reporting of the number needed
to treat (NNT) and the absolute risk reduction (ARR) in RCTs.
Methods Five frequently cited journals were investigated: Annals of Internal Medicine, BMJ, JAMA, The Lancet, and the New England Journal
of Medicine. For each journal, 4 years were evaluated: 1989, 1992,
1995, and 1998. All issues of each journal for each year were reviewed manually.
Eligible articles were those in which an RCT was conducted on the use of a
medication showing a significant treatment effect. Elements abstracted from
each eligible article were the condition investigated, event being treated
or prevented, intervention, study results, and reporting methods (relative
risk reduction, NNT, and ARR).
Results Of 359 eligible articles, NNT was reported in 8 articles. Six of the
8 studies were from 1998. Absolute risk reduction was reported in 18 articles,
10 of which were from 1998.
Conclusions Despite CONSORT recommendations, few authors expressed their findings
in terms of NNT or ARR. Consideration should be given to including these values
in reports of RCTs.
Randomized controlled trials (RCTs) are the gold standard in the assessment
of a treatment effect.1 The magnitude of this
effect can be presented in various ways, eg, relative risk reduction (RRR),
absolute risk reduction (ARR), and odds ratio (OR). In 1988, Laupacis et al2 reported the number needed to treat (NNT), an expression
of the number of patients who must be treated to prevent one adverse event.
Mathematically, NNT equals the reciprocal of the ARR. Reporting this value
provides readers with additional information to help them decide whether a
treatment should be used. Failing to report NNT may influence the interpretation
of study results. For example, reporting RRR alone may lead a reader to believe
that a treatment effect is larger than it really is.3- 6
We examined the frequency of explicit reporting of NNT and ARR in RCTs.
Five frequently cited journals were selected for investigation: Annals of Internal Medicine, BMJ, JAMA, The Lancet, and the New England Journal
of Medicine. For each journal, 4 years were assessed: 1989, 1992, 1995,
and 1998. The index year was designated 1989 because it represented 1 year
after publication on NNT by Laupacis et al.2
Three-year intervals were selected to obtain a representative sample to observe
for changes over time. All issues of each journal were manually reviewed for
the specific years of interest. Eligible articles included studies that reported
a randomization process, presented binary outcome or survival data, and reported
a statistically significant treatment effect. All eligible articles were reviewed
independently by 2 of the authors. A data collection form was used to abstract
the following information from each article: condition investigated, event
being treated or prevented, intervention, study results, and reporting methods
(RRR, NNT, and ARR). The complete article was reviewed to assess the use of
NNT and ARR. After completing the data abstraction process, findings were
There was complete agreement between the 2 reviewers. The summary of
findings and journal-specific results is presented in Table 1. Five hundred sixty-four articles met the criteria for a
randomized trial. Of these, 359 met the additional inclusion criteria. The
NNT was reported in 8 articles, and ARR was reported in 18. All 8 articles
reporting NNT also presented ARR. Six of the 8 studies reporting NNT and 10
of the 18 reporting ARR were from 1998.
The best evidence on the efficacy of medical interventions comes from
well-conducted RCTs, but unless the results of such trials are reported adequately,
assessing that information is difficult. The methods by which data are displayed
can influence the interpretation of the study results.3
The widespread practice of stressing important findings from RCTs in terms
of RRRs may potentially mislead the reader.4
The NNT and ARR express efficacy by incorporating the baseline risk without
therapy and the risk reduction with therapy. Also, NNT allows physicians to
understand how much effort is needed to prevent one event, thus allowing comparisons
with the amount of effort needed to prevent the same or other events in patients
with other disorders.
Despite NNT's potential, there have been concerns expressed about its
limitations. Cook and Sackett5 note that NNT
presents a problem when the results of an RCT with patients at one baseline
risk are applied to a particular patient at a different risk. Chatellier et
al6 express concern on extrapolating NNT to
time points not considered in trials.
There have been ongoing efforts to improve the quality of reporting
results of RCTs, including the Consolidated Standards of Reporting Trials
(CONSORT) statement, first published in 1996.7
A subsequent revision of the CONSORT statement encouraged reporting of absolute
values and NNT.8 Although the use of CONSORT
improves the quality of reporting in some areas,9
the results of our study raise concerns, specifically, that NNT and ARR are
underused in the medical literature. These results are consistent with those
of similar studies showing that inadequate description of randomization10 and participant flow11
are common. Junker12 described the adherence
to published standards of reporting on an 18-item scale; the mean score among
121 reports was 8.4. The results of our study and others suggest the need
for additional measures to ensure compliance with reporting standards. These
measures should continue to improve the reporting of an RCT and enable readers
to better interpret the results.
Nuovo J, Melnikow J, Chang D. Reporting Number Needed to Treat and Absolute Risk Reduction in Randomized Controlled Trials. JAMA. 2002;287(21):2813-2814. doi:10.1001/jama.287.21.2813