Survey of randomised trials indexed in PubMed in December 2006
The Cochrane highly sensitive search strategy identified 1735 citations that possibly linked to reports of randomised trials. After screening the titles and abstracts of all retrieved citations, we reviewed 879 full text articles and identified 616 primary reports of randomised trials for inclusion in our final cohort (fig 1). General and methodological characteristics were stratified by trial design. In 2006, 316 different journals published primary trial reports, with 25 journals publishing five or more randomised trials in the single month studied. The majority of trial reports were published in specialty journals (555/616 (90%)). The highest number of reports appeared in the American Journal of Cardiology (n=9), Anesthesia & Analgesia (n=9), Journal of the American College of Cardiology (n=9), New England Journal of Medicine (n=8), Journal of Clinical Oncology (n=7), and Journal of Infectious Diseases (n=7). All these journals are monthly apart from the New England Journal of Medicine, which is weekly.
Fig 1 Identification of randomised trials from PubMed citations indexed in December 2006
Table 1 provides information on general trial characteristics. Over three quarters (477/616 (78%)) of reports were of parallel group trials, 16% (100/616) were crossover trials, and the remaining 6% (39/616) were classified as “other”—more specifically, cluster randomised (13/39), factorial (10/39), or split body (16/39) trials. More than half (356/616 (58%)) of the trials investigated drugs as the primary intervention of interest, whereas 21% (128/616) assessed surgical or procedural interventions, 18% (113/616) assessed counselling or lifestyle interventions, and 3% (19/616) assessed equipment or devices. Forty per cent (248/616) of reports explicitly stated that the trial was conducted at a single centre and 28% (172/616) stated that the trial took place at multiple centres; the number of study centres was not explicitly defined in the remaining reports (196/616 (32%)). The median number of participants recruited per trial was 62 (10th to 90th percentile 19 to 392). As expected, parallel group trials were larger (median 80, 10th to 90th percentile 28 to 418) than crossover trials (median 20, 10th to 90th percentile 9 to 61).
Table 1 General characteristics of randomised trials indexed in PubMed in December 2006
Table 2 provides information on the reporting of methodological items. A third (205/616 (33%)) of all trial reports stated that the study was randomised in the study title, 53% (324/616) defined the primary outcome, and 45% (279/616) stated that a sample size calculation had been undertaken. The method used to generate the random sequence for allocating participants to study groups was reported in just over a third (209/616 (34%)) of trial reports, and a quarter (156/616 (25%)) reported the method used to prevent the person enrolling participants from knowing or predicting the allocation sequence.
Table 2 Reporting of methodological characteristics for randomised trials indexed in PubMed in December 2006
Fifty-nine per cent (362/616) of publications reported details of any blinding. Of these, 44% (160/362) provided specific details on who was blinded after assignment to interventions (for example, study participants, outcome assessors, care providers), whereas the remaining 56% (202/362) simply used the terms “blinded,” “single blind,” or “double blind” without providing further details. In addition to reporting who was blinded, 41% (254/616) of trial reports provided information on how blinding was achieved; of these, 45% (113/254) specifically described any similarities between the interventions or procedures (for example, identical in size, colour, and taste), whereas the remaining 55% (141/254) simply used the term “placebo” without providing further details.
A participant flow diagram depicting, for each group, the number of participants who were randomly assigned, received the intended treatment, and were analysed for the primary outcome was included in 28% (172/616) of study reports. Sixty-nine per cent (422/616) of trials reported details of any loss of follow-up for each study group; of these, 86% (362/422) explicitly stated the reasons for attrition or reported that there was no loss to follow-up. A third (188/616 (31%)) of trial reports stated that an intention to treat analysis had been carried out. Very few trial reports provided details of trial registration (58/616 (9%)) or where the original trial protocol could be accessed (9/616 (1%)). Details of funding sources were provided in 62% (380/616) of trial reports: 17% (107/616) of trials were funded solely by industry, 11% (70/616) were part funded by industry, and 32% (196/616) were not industry funded. For all trials, the quality of reporting was generally poorer for crossover trials than for parallel group trials (table 2).
Comparison of randomised trials indexed in PubMed in 2000 with those indexed in 2006
In both 2000 and 2006, the majority of trials involved two study arms (379/519 (73%) in 2000 v 468/616 (76%) in 2006), had parallel group design (383/519 (74%) v 477/616 (78%)), with a median of 80 participants per trial, and were published in specialty journals (482/519 (93%) v 555/616 (90%)). The proportion of articles that reported drug trials decreased between 2000 and 2006 (from 393/519 (76%) to 356/616 (58%)), whereas the proportion of surgical trials increased (from 51/519 (10%) to 128/616 (21%); table 3).
Table 3 Reporting of general characteristics for randomised trials indexed in PubMed in 20004 compared with those indexed in 2006
We identified an increase between 2000 and 2006 in the proportion of trial reports that included details of the primary outcome (RR 1.18, 95% CI 1.04 to 1.33; AD 8%, 95% CI 2% to 14%), sample size calculation (RR 1.66, 95% CI 1.40 to 1.95; AD 18%, 95% CI 12% to 23%), and the methods of random sequence generation (RR 1.62, 95% CI 1.32 to 1.97; AD 13%, 95% CI 8% to 18%) and allocation concealment (RR 1.40, 95% CI 1.11 to 1.76; AD 7%, 95% CI 2% to 12%). There was no difference in the proportion of trials that provided specific details on who was blinded after assignment to interventions (RR 0.91, 95% CI 0.75 to 1.10; AD −3%, 95% CI −8% to 3%; fig 2).
Fig 2 Differences in reporting of methodological items between 2000 and 2006
Comparison of journals endorsing the CONSORT Statement with non-endorsing journals in 2006
We also compared the quality of reporting for randomised trials indexed in journals that endorse the CONSORT Statement with those in non-endorsing journals for reports published in December 2006. We identified a significantly higher rate of reporting of key methodological items in CONSORT endorsing journals (fig 3). Interestingly, we observed that the proportion of trial reports that provided specific details on who was blinded after assignment to interventions was higher in CONSORT endorsing journals (RR 1.53, 95% CI 1.17 to 1.99; AD 11%, 95% CI 4% to 18%), and a reverse scenario was true for those reports that used the terms “blinded,” “single blind,” or “double blind” (RR 0.93; 95% CI 0.74 to 1.16; AD −3%, 95% CI −10% to 5%).
Fig 3 Differences in reporting of methodological items between CONSORT endorsing and non-endorsing journals in 2006