Psychiatric Bulletin (2007) 31: 265-267. doi: 10.1192/pb.bp.106.012104
© 2007 The Royal College of Psychiatrists
Use of statistics in the Psychiatric Bulletin: author guidelines
M. Sayeed Haque, Statistician
Department of Psychiatry, University of Birmingham, Edgbaston, Birmingham
B15 2QZ, email:
m.s.haque{at}bham.ac.uk
Sanju George
Specialist Registrar in Psychiatry, Queen Elizabeth Psychiatric Hospital,
Edgbaston, Birmingham B15 2QZ
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Introduction
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Inappropriate use of statistics can seriously undermine the validity of
published medical research. This paper aims to make recommendations to authors
on the use and presentation of statistics in submissions to the
Psychiatric Bulletin. We derive our recommendations from a review of
the quality of statistical reporting in 50 consecutive ‘original’
papers published in the Psychiatric Bulletin. However simple the
methodology of a study, adequate emphasis needs to be given to the correct and
appropriate use and presentation of statistics in scientific papers.
Appropriate use of statistics is crucial in medical research. Use of
inappropriate statistical methods and/or faulty interpretation of results can
alter research findings significantly. Studies of statistical errors in
published medical research have found statistical error rates in the region of
30-75% (Pocock et al,
1987; McGuigan,
1995). McGuigan
(1995) looked at the use of
statistics in papers published in the British Journal of Psychiatry
over a 1-year period and found that nearly 40% of papers contained statistical
errors. More worryingly, he found that these rates were very similar to those
noted in an earlier study by White
(1979), and concluded that
there was no evidence of a change in the statistical error rate over that
period (1977-1993).
Authors, reviewers and editors all have crucial roles to play, at different
stages of a paper's pre-publication ‘journey’, in ensuring the
statistical quality and rigour of published papers. The aim of this paper is
to provide recommendations to prospective authors in their use of statistics
in papers submitted to the Psychiatric Bulletin. In order to best
tailor this guidance to potential contributors to the Psychiatric
Bulletin, we based it on the findings of an analysis of the statistical
reporting in 50 papers published in the Psychiatric Bulletin in 2003.
As detailed guidelines for authors on the use of statistics in medical
research are easily available (see Box 1), rather than reinvent the wheel, we
have attempted to tailor our recommendations to address the simple statistics
that are relevant and appropriate to papers in the Psychiatric
Bulletin.
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Method
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The Psychiatric Bulletin was hand searched for 50 consecutive
‘original’ papers published in 2003 (starting with the January
2003 issue). Papers published in this section (i.e. ‘original
papers’) were included in the study as they were most likely to have
used and presented statistical analyses than papers published in other
sections in the journal. We looked at each paper to identify statistical
errors, that is, errors in the use and presentation of statistics. For the
purpose of this paper, we took ‘statistical error’ to mean any of
the following: inappropriate choice of statistical methods, incorrect use of
statistical tests, faulty interpretation of results and errors in presentation
of statistics as used by Hand & Sham
(1995).
| Box 1. Useful references for statistical guidelines for authors
- BMJ advice on statistical methods
(http://resources.bmj.com/bmj/authors/special-methods)
- Balilar, J. C. & Mosteller, F. (1988) Guidelines for statistical
reporting in articles for medical journals. Annals of Internal
Medicine, 108, 266-273.
- Wilkinson, L. & Task Force on Statistical Inference, APA Board of
Scientific Affairs (1999) Statistical methods in psychology journals:
guidelines and explanations. American Psychologist, 54,
594-604.
- International Committee of Medical Journal Editors website
(http://www.icmje.org/icmje.pdf)
- See instructions for authors section in major psychiatric journals.
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Results
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Tables 1,
2,
3 show the types of study
design, statistical procedures used and the number of papers using different
statistical methods respectively.
Examples of errors in use and presentation of statistics
Here we present some examples of errors in use and presentation of
statistics in the papers looked at. These included
- no mention in the Method section as to what statistical methods were
used
- mean value reported but standard deviation not given
- t-test used but did not mention which one (i.e. one-sample
t-test or two independent samples t-test or two paired
samples t-test)
- reported ‘no significant difference’ but no P value
quoted
- P values quoted but no tests mentioned
- analysis of variance (ANOVA) used but degrees of freedom (d.f.) not
stated
- mean value reported as ‘mean ±’ with no clarification of
what ± means (i.e. standard deviation or standard error).
A large majority of the studies (82%) were questionnaire surveys or case
note-based studies. Only 5 out of 50 original studies involved direct patient
contact (see Table 1). The
simplicity of the study designs and methodology reflected the type of
statistical tests used in these studies: mostly descriptive statistics and
simple tests of significance (see Tables
2 and
3). The most commonly used
tests were the 
2-test (16 papers) and the t-test (9
papers). This is consistent with research findings from psychiatric and
non-psychiatric medical literature (Elster,
1994; Rigby et al,
2004). Reed et al
(2003) studied the use of
statistics in six medical journals and noted that 2-test and
t-test were the most commonly used tests. They went on to argue that
clinicians could satisfactorily interpret 70% of medical literature if they
understood descriptive statistics, chi-squared test and t-test.
Although this statement may be an over-simplification, the underlying message
may be particularly relevant to authors and readers of the Psychiatric
Bulletin.
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Recommendations to authors in their use and presentation of statistics
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Based on the results described above, we make some simple recommendations
on the appropriate use and presentation of statistics for authors submitting
papers to the Psychiatric Bulletin. We suggest that these
recommendations be read in conjunction with more detailed guidelines published
elsewhere (see Box 1).
General
- Mention/explain the statistical methods used in the Method section of your
paper (as a separate paragraph if appropriate)
- Mention the statistical software used in analysing the data
- Draw only justifiable conclusions from the results
- Avoid overuse of statistical abbreviations
- If uncommon statistical tests are used, provide reference
- If a statistician has helped with the study, it is good practice to
acknowledge their contribution as appropriate.
Presentation of results
- Avoid duplication of data in text and table/graph
- No value reported should have more than 2 decimal places
- Where possible, exact P values should be quoted rather than merely
stating ‘a significant result was found’ or
‘P<0.05’
- If the statistical software output shows that the P value is equal
to 0.000, then report that the P value is smaller than 0.001 or
P<0.001
- Whenever the mean value is reported it is good practice to also report with
it the standard deviation or the standard error, and clarify which measure is
being reported. For example, mean12.3 (s.d.=2.6).
Use of statistics
- If using descriptive statistics, report values appropriately (i.e. for
continuous data report mean and standard deviation and for discrete data quote
median and interquartile range or range)
- If using the 2-test, it should be justified. Note that if
the expected cell frequency is less than 5 in 20% or more of the cells, then
the 2-test is not valid
- Whenever the t-test is used, the type should be mentioned (i.e.
independent samples t-test or paired samples t-test (if
using the independent samples t-test, it should also be mentioned
whether equality of variance or inequality of variance was used)
- Use of parametric tests such as the t-test and ANOVA should be
justified (i.e. the data follow normal distribution)
- Use appropriate statistical analyses to answer the research question under
study.
Authors should ‘describe statistical methods with enough detail to
enable a knowledgeable reader with access to the original data to verify the
reported results’
(http://www.icmje.org/icmje.pdf).
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Conclusions
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Inappropriate use of statistics can seriously undermine the validity of
published medical research. However simple the methodology of a study,
adequate emphasis needs to be given to the correct and appropriate use and
presentation of statistics in scientific papers.
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References
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ELSTER, A. D. (1994) Use of statistical analysis in
the AJR and Radiology: frequency, methods and subspecialty differences.
American Journal of
Radiology,163, 711
-715.HAND, D. & SHAM, P. (1995) Improving the quality
of statistics in psychiatric research. British Journal of
Psychiatry, 167, 689
-691.[Free Full Text]
McGUIGAN, S. M. (1995) The use of statistics in the
British Journal of Psychiatry. British Journal of
Psychiatry, 167, 683
-688.[Abstract/Free Full Text]
POCOCK, S. J., HUGHES, M. D. & LEE, R. J. (1987)
Statistical problems in the reporting of clinical trials. A survey of
three medical journals. New England Journal of Medicine,
317, 426
-432.
REED, J. F., 3rd, SALEN, P. & BAGHER, P. (2003)
Methodological and statistical techniques: what do residents really need to
know about statistics? Journal of Medical Systems,
27, 233
-238.[CrossRef][Medline]
RIGBY, A. S., ARMSTRONG, G. K., CAMPBELL, M. J., et al
(2004) A survey of statistics in three UK general practice
journals. Biomed Central: Medical Research
Methodology, 4, 4
-28.[Medline]
WHITE, S. J. (1979) Statistical errors in papers in
the British Journal of Psychiatry. British Journal of
Psychiatry, 135, 336
-342.[Abstract/Free Full Text]
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Introduction
Method