Publication bias in blood and marrow transplantation

Full publication of results initially presented in abstracts

BACKGROUND

Abstracts of presentations at scientific meetings are usually available only in conference proceedings. If subsequent full publication of results reported in these abstracts is based on the magnitude or direction of the results, publication bias may result. Publication bias creates problems for those conducting systematic reviews or relying on the published literature for evidence about health and social care.

OBJECTIVES

To systematically review reports of studies that have examined the proportion of meeting abstracts and other summaries that are subsequently published in full, the time between meeting presentation and full publication, and factors associated with full publication.

SEARCH METHODS

We searched MEDLINE, Embase, the Cochrane Library, Science Citation Index, reference lists, and author files. The most recent search was done in February 2016 for this substantial update to our earlier Cochrane Methodology Review (published in 2007).

SELECTION CRITERIA

We included reports of methodology research that examined the proportion of biomedical results initially presented as abstracts or in summary form that were subsequently published. Searches for full publications had to be at least two years after meeting presentation.

DATA COLLECTION AND ANALYSIS

Two review authors extracted data and assessed risk of bias. We calculated the proportion of abstracts published in full using a random-effects model. Dichotomous variables were analyzed using risk ratio (RR), with multivariable models taking into account various characteristics of the reports. We assessed time to publication using Kaplan-Meier survival analyses.

MAIN RESULTS

Combining data from 425 reports (307,028 abstracts) resulted in an overall full publication proportion of 37.3% (95% confidence interval (CI), 35.3% to 39.3%) with varying lengths of follow-up. This is significantly lower than that found in our 2007 review (44.5%. 95% CI, 43.9% to 45.1%). Using a survival analyses to estimate the proportion of abstracts that would be published in full by 10 years produced proportions of 46.4% for all studies; 68.7% for randomized and controlled trials and 44.9% for other studies. Three hundred and fifty-three reports were at high risk of bias on one or more items, but only 32 reports were considered at high risk of bias overall.Forty-five reports (15,783 abstracts) with 'positive' results (defined as any 'significant' result) showed an association with full publication (RR = 1.31; 95% CI 1.23 to 1.40), as did 'positive' results defined as a result favoring the experimental treatment (RR =1.17; 95% CI 1.07 to 1.28) in 34 reports (8794 abstracts). Results emanating from randomized or controlled trials showed the same pattern for both definitions (RR = 1.21; 95% CI 1.10 to 1.32 (15 reports and 2616 abstracts) and RR = 1.17; 95% CI, 1.04 to 1.32 (13 reports and 2307 abstracts), respectively.Other factors associated with full publication include oral presentation (RR = 1.46; 95% CI 1.40 to 1.52; studied in 143 reports with 115,910 abstracts); acceptance for meeting presentation (RR = 1.65; 95% CI 1.48 to 1.85; 22 reports with 22,319 abstracts); randomized trial design (RR = 1.51; 95% CI 1.36 to 1.67; 47 reports with 28,928 abstracts); and basic research (RR = 0.78; 95% CI 0.74 to 0.82; 92 reports with 97,372 abstracts). Abstracts originating at an academic setting were associated with full publication (RR = 1.60; 95% CI 1.34 to 1.92; 34 reports with 16,913 abstracts), as were those considered to be of higher quality (RR = 1.46; 95% CI 1.23 to 1.73; 12 reports with 3364 abstracts), or having high impact (RR = 1.60; 95% CI 1.41 to 1.82; 11 reports with 6982 abstracts). Sensitivity analyses excluding reports that were abstracts themselves or classified as having a high risk of bias did not change these findings in any important way.In considering the reports of the methodology research that we included in this review, we found that reports published in English or from a native English-speaking country found significantly higher proportions of studies published in full, but that there was no association with year of report publication. The findings correspond to a proportion of abstracts published in full of 31.9% for all reports, 40.5% for reports in English, 42.9% for reports from native English-speaking countries, and 52.2% for both these covariates combined.

AUTHORS' CONCLUSIONS

More than half of results from abstracts, and almost a third of randomized trial results initially presented as abstracts fail to be published in full and this problem does not appear to be decreasing over time. Publication bias is present in that 'positive' results were more frequently published than 'not positive' results. Reports of methodology research written in English showed that a higher proportion of abstracts had been published in full, as did those from native English-speaking countries, suggesting that studies from non-native English-speaking countries may be underrepresented in the scientific literature. After the considerable work involved in adding in the more than 300 additional studies found by the February 2016 searches, we chose not to update the search again because additional searches are unlikely to change these overall conclusions in any important way.

Is publication bias present in gastroenterological research? An analysis of abstracts presented at an annual congress

Background

Publication bias is the tendency of investigators, reviewers, and editors to submit or accept manuscripts for publication based on their direction or strength of findings. In this study, we investigated if publication bias was present in gastroenterological research by evaluating abstracts at Americas Hepato-Pancreato-Biliary Congresses from 2011 to 2013.

Methods

We searched Google, Google Scholar, and PubMed to locate the published reports of research described in these abstracts. If a publication was not found, a second investigator searched to verify nonpublication. If abstract publication status remained undetermined, authors were contacted regarding reasons for nonpublication. For articles reaching publication, the P value, study design, time to publication, citation count, and journals in which the published report appeared were recorded.

Results

Our study found that of 569 abstracts presented, 297 (52.2%) reported a P value. Of these, 254 (85.5%) contained P values supporting statistical significance. The abstracts reporting a statistically significant outcome were twice as likely to reach publication than abstracts with no significant findings (OR 2.10, 95% CI [1.06–4.14]). Overall, 243 (42.7%) abstracts reached publication. The mean time to publication was 14 months and a median time of nine months.

Conclusion

In conclusion, we found evidence for publication bias in gastroenterological research. Abstracts with significant P values had a higher probability of reaching publication. More than half of abstracts presented from 2011 to 2013 failed to reach publication. Readers should take these findings into consideration when reviewing medical literature.

A systematic review of the processes used to link clinical trial registrations to their published results

BACKGROUND

Studies measuring the completeness and consistency of trial registration and reporting rely on linking registries with bibliographic databases. In this systematic review, we quantified the processes used to identify these links.

METHODS

PubMed and Embase databases were searched from inception to May 2016 for studies linking trial registries with bibliographic databases. The processes used to establish these links were categorised as automatic when the registration identifier was available in the bibliographic database or publication, or manual when linkage required inference or contacting of trial investigators. The number of links identified by each process was extracted where available. Linear regression was used to determine whether the proportions of links available via automatic processes had increased over time.

RESULTS

In 43 studies that examined cohorts of registry entries, 24 used automatic and manual processes to find articles; 3 only automatic; and 11 only manual (5 did not specify). Twelve studies reported results for both manual and automatic processes and showed that a median of 23% (range from 13 to 42%) included automatic links to articles, while 17% (range from 5 to 42%) of registry entries required manual processes to find articles. There was no evidence that the proportion of registry entries with automatic links had increased (R ² = 0.02, p = 0.36). In 39 studies that examined cohorts of articles, 21 used automatic and manual processes; 9 only automatic; and 2 only manual (7 did not specify). Sixteen studies reported numbers for automatic and manual processes and indicated that a median of 49% (range from 8 to 97%) of articles had automatic links to registry entries, and 10% (range from 0 to 28%) required manual processes to find registry entries. There was no evidence that the proportion of articles with automatic links to registry entries had increased (R ² = 0.01, p = 0.73).

CONCLUSIONS

The linkage of trial registries to their corresponding publications continues to require extensive manual processes. We did not find that the use of automatic linkage has increased over time. Further investigation is needed to inform approaches that will ensure publications are properly linked to trial registrations, thus enabling efficient monitoring of trial reporting.

Publication bias in pediatric hematology and oncology: analysis of abstracts presented at the annual meeting of the American Society of Pediatric Hematology and Oncology

Publication bias (PB) is a threat to the validity of medical literature, and has not been studied in the field of pediatric hematology/oncology. We analyzed the abstracts presented at the 2005 American Society of Pediatric Hematology/Oncology annual meeting to assess for PB. Abstracts were categorized by type of research, number of centers, funding status, presentation format, sample size, statistical significance, and the direction of results. Publication status was determined by searching PubMed. Thirty nine abstracts (51%) were categorized as clinical studies, 67 (36%) as basic research, and 24 (13%) as others. One hundred and twenty three abstracts (67%) were considered to have positive results, 14 (8%) negative results, and 47 (25%) with neutral or not stated results. About 62% of the abstracts were published in peer-reviewed journals at a median time to publication of 19 months (IQR = 11-29 months). Abstracts with positive results were more likely to get published than others (combined negative and neutral results) (P = .002). Factors like sample size, number of centers, or statistical significance reporting did not affect the publication rate. Our data suggests the existence of PB in the field of pediatric hematology/oncology. Still, further analysis of other international meetings is needed to validate our findings.

Publication bias in neuroimaging research: implications for meta-analyses

Neuroimaging and the neurosciences have made notable advances in sharing activation results through detailed databases, making meta-analysis of the published research faster and easier. However, the effect of publication bias in these fields has not been previously addressed or accounted for in the developed meta-analytic methods. In this article, we examine publication bias in functional magnetic resonance imaging (fMRI) for tasks involving working memory in the frontal lobes (Brodmann Areas 4, 6, 8, 9, 10, 37, 45, 46, and 47). Seventy-four studies were selected from the literature and the effect of publication bias was examined using a number of regression-based techniques. Pearson's r correlation coefficient and Cohen's d effect size estimates were computed for the activation in each study and compared to the study sample size using Egger's regression, Macaskill's regression, and the 'Trim and Fill' method. Evidence for publication bias was identified in this body of literature (p < 0.01 for each test), generally, though was neither task- nor sub-region-dependent. While we focused our analysis on this subgroup of brain mapping studies, we believe our findings generalize to the brain imaging literature as a whole and databases seeking to curate their collective results. While neuroimaging databases of summary effects are of enormous value to the community, the potential publication bias should be considered when performing meta-analyses based on database contents.

Publication bias is present in blood and marrow transplantation: an analysis of abstracts at an international meeting

Publication bias is the preferential publication of research with positive results, and is a threat to the validity of medical literature. Preliminary evidence suggests that research in blood and marrow transplantation (BMT) lacks publication bias. We evaluated publication bias at an international conference, the 2006 Center for International Blood and Marrow Transplant Research (CIBMTR)/American Society for Blood and Marrow Transplantation (ASBMT) "tandem" meeting. All abstracts were categorized by type of research, funding status, number of centers, sample size, and direction of the results. Publication status was then determined for the abstracts by searching PubMed. Of 501 abstracts, 217 (43%) were later published as complete manuscripts. Abstracts with positive results were more likely to be published than those with negative or unstated results (P = .001). Furthermore, positive studies were published in journals with a mean impact factor of 6.92, whereas journals in which negative/unstated studies were published had an impact factor of only 4.30 (P = .02). We conclude that publication bias exists in the BMT literature. Full publication of research, regardless of direction of results, should be encouraged and the BMT community should be aware of the existence of publication bias.