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The graphical display of data is among the most powerful tools available for communicating medical research findings, given the increasing complexity of study designs and the mind's preference for information conveyed in pictorial format. 1 2 However, although general information is available on what constitutes an effective data display 1 2 3 4 5 6 and what constitutes good practice in reporting trials, 7 8 there is relatively little guidance on using figures to aid the presentation of trial results. 9
Because figures are so effective in creating an enduring impression of results, their construction-and interpretation by readers-must be handled with care. We recently conducted a survey to determine the types of figures used most commonly in reports of clinical trials and to uncover the good, and not so good, practices that typically attend their use. 10 Here, we highlight the important features of the most commonly used types of figures. In doing so, we hope to illustrate the hallmarks of figures that are likely to convey an impression consistent with valid trial conclusions and those aspects of figures that may, without careful interpretation, be misleading.
What comes up most
We examined all issues of five major general medical journals (Annals of Internal Medicine, BMJ, JAMA, Lancet, and New England Journal of Medicine ) published from November 2006 to January 2007. The 77 reports of randomised trials included in these journal issues contained 175 figures (mean 2.3 figures per article). The four most common types of figure were flow diagrams (66 articles), Kaplan-Meier plots (32 articles), forest plots (21 articles), and repeated measures plots (20 articles) (table ). 10
No of articles (n=77) | |
Journal | |
Annals of Internal Medicine | 7 |
BMJ * | 16 |
JAMA | 14 |
Lancet | 12 |
New England Journal of Medicine | 28 |
Type of figure[dagger] | |
Flow diagram | 66 |
Kaplan Meier plot | 32 |
Forest plot | 21 |
Repeated measures | 20 |
Bar chart | 7 |
Individual patient data | 3 |
Box plot | 2 |
Cumulative distribution | 1 |
*Online version.
[dagger]Some articles had one type of figure several times. Each type of figure is counted only once per article.
Flow diagrams
Flow diagrams are integral to the CONSORT guidelines for the reporting of clinical trials. 7 8 They display the flow of participants through the stages of the trial in a...