Minimally invasive treatments for benign prostatic enlargement: systematic review of randomised controlled trialsBMJ 2008; 337 doi: https://doi.org/10.1136/bmj.a1662 (Published 09 October 2008) Cite this as: BMJ 2008;337:a1662
All rapid responses
We thank Gibson[Gibson 2008] for raising the important question about
whether or not data from abstracts should be included in systematic
Our paper[Lourenco 2007] reported on the clinical effectiveness of
minimally invasive treatments for benign prostatic enlargement (BPE),
which was part of a large Health Technology Assessment (HTA) report that
aimed to evaluate the clinical and cost-effectiveness for all
interventional treatments for BPE. It was agreed at the outset of the
review that abstracts of conference proceedings of RCTs would be searched
for because they can potentially lead to the identification of additional
trials for inclusion in the systematic review. It was decided that any
data available in abstracts would not be included in the review because of
concern about data quality and likely overlap with some published reports.
Due to time and resource limitations, no attempt would be made to obtain
additional data from the authors of the abstracts.
Nevertheless, when we undertook the review, we were concerned by the
large number of abstracts identified and the possible publication bias
that they might introduce. For this reason, we conducted a subsidiary
study to investigate this. [Wong 2007] From the original literature search
for the HTA report – it seemed that 67 abstracts (linked to 48 different
first authors) had never been published in full as peer-reviewed journal
articles. We performed a comprehensive PubMed and Google search for the
contact details of these authors and contacted them by post and e-mail,
and in some cases, phone calls. These authors were invited to complete a
questionnaire aiming to elucidate the reasons for their abstract failing
to be published as a full article, and invited them to volunteer any extra
study data. A total of 47 questionnaires (linked to 47 study abstracts)
were responded to; 32 out of the 47 abstracts had in fact been fully
reported and all were already included in the systematic review (though we
had not been able to link them from the information available in the
abstract), with the exception of those abstracts that were published after
our last searching date (n=7). This illustrates a deficiency of current
documentation or search strategy in linking conference abstracts with
subsequent full text publication that needs to be addressed although it is
reassuring that most were included despite the link not being apparent.
The principal reason for non-full reporting was ‘being written up’.
We also conducted a sensitivity analysis, to investigate the
potential impact of the addition of data from the 67 abstracts. A majority
of the data (59 abstracts) reported in the abstracts lacked the necessary
statistical details (standard deviations, standard errors and confidence
intervals) and rendered them unsuitable for the analysis. We found that
inclusion of useable abstract data had no significant impact on any of the
These findings reassured us: firstly, exclusion of data from
abstracts was justified because of duplication and quality concerns; and
secondly, inclusion of the few useable data that were available did not
materially alter the findings.
Gibson L.M. Failing to include data from unpublished trials limits
the findings of systematic reviews. Rapid response. BMJ.com (12th October
Lourenco T, Pickard R, Vale L, Grant A, Fraser C, MacLennan G, N’Dow
J, Benign Prostatic Enlargement Team. Minimally invasive treatments for
benign prostatic enlargement: systematic review of randomised controlled
trials BMJ 2008, 337:a1662.
Wong S.S.W. The fate of conference abstracts: A side-arm study for
the systematic review and economic modelling of clinical effectiveness and
cost-utility of surgical treatments for men with benign prostatic
enlargement (BPE): A dissertation towards an MSc Health Services and
Public Health Research. University of Aberdeen; July 2007
Competing interests: No competing interests
Lourenco et al. have addressed an important and relevant clinical
question with their recent systematic review of trials of minimally
invasive treatments for benign prostatic enlargement(1). However, their
findings should be interpreted cautiously.
Lourenco et al. performed a comprehensive search strategy to identify
both published and unpublished reports of relevant trials which included
searching conference proceedings(1). Although they used the most
comprehensive report of a trial to extract data, they excluded trials
which were only available in abstract form, which leads me to question why
the authors searched the conference proceedings in the first place.
In total, 22 randomised controlled trials were included in their
review, but a further 53 were excluded because they were only reported in
abstracts(1). Lourenco et al. recognise that excluding these unpublished
trials may have introduced bias into their review(1), but they did not
attempt to contact the authors of these numerous unpublished trials for
more data. With additional data, some of these trials could have been
included in the review, which would have reduced bias and improved the
accuracy of the estimate of the effects of minimally invasive treatments
for benign prostatic enlargement. The contact details of authors of
abstracts can be found by searching Medline and Embase for the authors’
names and retrieving articles which report their contact details. An
author’s institutional affiliations can be cross-referenced between the
abstract and the articles to ensure that both sources refer to the same
There are well documented cases in the literature which demonstrate
that the addition of data from unpublished trials can change the findings
of systematic reviews. Whittington et al. found that published trials of
paroxetine for depression in 5-18 year olds showed a neutral to weakly
positive effect. When data from unpublished trials was also included, the
risks of adverse effects and suicidal ideation and suicide attempts
outweighed the benefits of paroxtine in this group of patients(3).
Further work which includes data from unpublished trials is needed
before we can draw reliable conclusions about the effects of minimally
invasive treatments for benign prostatic enlargement.
(1) Lourenco T, Pickard R, Vale L, Grant A, Fraser C, MacLennan G et
al. Minimally invasive treatments for benign prostatic enlargement:
systematic review of randomised controlled trials. BMJ 2008; 337:a1662.
(2) Sanossian N, Ohanian AG, Saver JL, Kim LI, Ovbiagele B. Frequency
and determinants of nonpublication of research in the stroke literature.
Stroke 2006; 37(10):2588-2592.
(3) Whittington CJ, Kendall T, Fonagy P, Cottrell D, Cotgrove A,
Boddington E. Selective serotonin reuptake inhibitors in childhood
depression: systematic review of published versus unpublished data. Lancet
Competing interests: No competing interests