Citations to trials of nicotine replacement therapy were biased toward positive results and high-impact-factor journals

The most 100 cited papers in addiction research on cannabis, heroin, cocaine and psychostimulants. A bibliometric cross-sectional analysis

The number of citations a peer-reviewed article receives is often used as a measure of its importance and scientific impact. This paper identifies, describes and categorizes the highly cited papers in addiction research on cannabis, heroin, cocaine and psychostimulants. Highly cited papers were identified in the Web of Science Core Collection database. Several bibliometric indicators were calculated. Social network analysis was applied to draw groups of authors and institutions with the greatest number of collaborations and co-words. The number of citations for the top 100 cited articles ranged from 649 to 4,672. The articles were published in 40 journals. The subject category Substance Abuse included 10 papers. The United States was the most productive country (79 papers), followed by the United Kingdom (9). The main funding institutions were the National Institutes of Health in the United States. The network of collaboration between authors distributes the 352 researchers into 53 groups. The three most cited works address the neural basis of drug craving as an incentive-sensitization theory of addiction, the clinical and research uses of the Addiction Severity Index, and the neurocircuitry of addiction. Scientific literature on addictions is widely dispersed both in multidisciplinary and specific journals of neurology, psychiatry and addictions, with relatively few publications providing most of the citations. An ongoing challenge for this field is the concentration of highly cited papers coming from a select number of countries, with the United States being the research hub of the world, with the highest volume of publications and total citations.

Citation bias in the literature on dietary trans fatty acids and serum cholesterol

OBJECTIVE

Balanced citations are a necessary condition for a sound development of scientific knowledge, whereas selective citations may bias scientific consensus. In this study, we assess which determinants influenced the likelihood of being cited in the literature on trans fatty acids and cholesterol.

STUDY DESIGN AND SETTING

We conducted a citation network analysis of the literature concerning trans fats and low density cholesterol and high density cholesterol. Each publication was scored on various potential determinants of citation, such as study outcome, study design, sample size, journal impact factor, and funding source. We applied random effect logistic regression to identify determinants of citation.

RESULTS

A network of 108 publications was identified, containing 5,041 potential citation paths and 669 utilized citation paths. Reporting statistically significant results was found to be a strong predictor of citation, together with sample size, journal impact factor, and the authority of the authors.

CONCLUSION

Within the literature on trans fat intake and cholesterol, selective citations are based on several grounds. Especially the effect of reporting significant results on citation requires special attention because disproportionate attention is paid to publications suggesting a harmful effect of trans fat on cholesterol.

Predictors of Citation Rate in Psychology: Inconclusive Influence of Effect and Sample Size

In the present article, we investigate predictors of how often a scientific article is cited. Specifically, we focus on the influence of two often neglected predictors of citation rate: effect size and sample size, using samples from two psychological topical areas. Both can be considered as indicators of the importance of an article and post hoc (or observed) statistical power, and should, especially in applied fields, predict citation rates. In Study 1, effect size did not have an influence on citation rates across a topical area, both with and without controlling for numerous variables that have been previously linked to citation rates. In contrast, sample size predicted citation rates, but only while controlling for other variables. In Study 2, sample and partly effect sizes predicted citation rates, indicating that the relations vary even between scientific topical areas. Statistically significant results had more citations in Study 2 but not in Study 1. The results indicate that the importance (or power) of scientific findings may not be as strongly related to citation rate as is generally assumed.

The impact factor of an open access journal does not contribute to an article's citations

Background

Citations of papers are positively influenced by the journal’s impact factor (IF). For non-open access (non-OA) journals, this influence may be due to the fact that high-IF journals are more often purchased by libraries, and are therefore more often available to researchers, than low-IF journals. This positive influence has not, however, been shown specifically for papers published in open access (OA) journals, which are universally accessible, and do not need library purchase. It is therefore important to ascertain if the IF influences citations in OA journals too.

Methods

203 randomized controlled trials (102 OA and 101 non-OA) published in January 2011 were included in the study. Five-year citations for papers published in OA journals were compared to those for non-OA journals. Source papers were derived from PubMed. Citations were retrieved from Web of Science, Scopus, and Google Scholar databases. The Thompson-Reuter’s IF was used.

Results

OA journals were found to have significantly more citations overall compared to non-OA journals (median 15.5 vs 12, p=0.039). The IF did not correlate with citations for OA journals (Spearman’s rho =0.187, p=0.60). The increase in the citations with increasing IF was minimal for OA journals (beta coefficient = 3.346, 95% CI -0.464, 7.156, p=0.084). In contrast, the IF did show moderate correlation with citations for articles published in non-OA journals (Spearman’s rho=0.514, p<0.001). The increase in the number of citations was also significant (beta coefficient = 4.347, 95% CI 2.42, 6.274, p<0.001).

Conclusion

It is better to publish in an OA journal for more citations. It may not be worth paying high publishing fees for higher IF journals, because there is minimal gain in terms of increased number of citations. On the other hand, if one wishes to publish in a non-OA journal, it is better to choose one with a high IF.

A manifesto for reproducible science

Improving the reliability and efficiency of scientific research will increase the credibility of the published scientific literature and accelerate discovery. Here we argue for the adoption of measures to optimize key elements of the scientific process: methods, reporting and dissemination, reproducibility, evaluation and incentives. There is some evidence from both simulations and empirical studies supporting the likely effectiveness of these measures, but their broad adoption by researchers, institutions, funders and journals will require iterative evaluation and improvement. We discuss the goals of these measures, and how they can be implemented, in the hope that this will facilitate action toward improving the transparency, reproducibility and efficiency of scientific research.

Citation bias and selective focus on positive findings in the literature on the serotonin transporter gene (5-HTTLPR), life stress and depression

BACKGROUND

Caspi et al.'s 2003 report that 5-HTTLPR genotype moderates the influence of life stress on depression has been highly influential but remains contentious. We examined whether the evidence base for the 5-HTTLPR-stress interaction has been distorted by citation bias and a selective focus on positive findings.

METHOD

A total of 73 primary studies were coded for study outcomes and focus on positive findings in the abstract. Citation rates were compared between studies with positive and negative results, both within this network of primary studies and in Web of Science. In addition, the impact of focus on citation rates was examined.

RESULTS

In all, 24 (33%) studies were coded as positive, but these received 48% of within-network and 68% of Web of Science citations. The 38 (52%) negative studies received 42 and 23% of citations, respectively, while the 11 (15%) unclear studies received 10 and 9%. Of the negative studies, the 16 studies without a positive focus (42%) received 47% of within-network citations and 32% of Web of Science citations, while the 13 (34%) studies with a positive focus received 39 and 51%, respectively, and the nine (24%) studies with a partially positive focus received 14 and 17%.

CONCLUSIONS

Negative studies received fewer citations than positive studies. Furthermore, over half of the negative studies had a (partially) positive focus, and Web of Science citation rates were higher for these studies. Thus, discussion of the 5-HTTLPR-stress interaction is more positive than warranted. This study exemplifies how evidence-base-distorting mechanisms undermine the authenticity of research findings.

Brief alcohol intervention trials conducted by higher prestige authors and published in higher impact factor journals are cited more frequently

OBJECTIVE

To examine the relationships between study quality, author prestige, journal impact factors, and citation rates of trials and to examine whether journal impact factors mediated the relationships between study quality and author prestige on citation rates.

STUDY DESIGN AND SETTING

We used bibliometric data from 128 controlled trials included in a recent meta-analysis on brief alcohol interventions for adolescents and young adults. We obtained the number of citations from ISI Web of Knowledge and Google Scholar; journal impact factors were obtained from ISI Web of Knowledge. Linear regression models were used to examine the direct and indirect effects of interest.

RESULTS

The results indicated that studies were published in journals with higher impact factors when first authors had higher h-indices and studies were funded, but this was largely because those studies were of higher quality. Studies were cited more frequently when first authors had higher h-indices and studies were funded, even after adjusting for study quality proxies. The observed associations between study quality and author prestige on citation rates were also partly mediated through journal impact factors.

CONCLUSION

We conclude that studies conducted by more established authors and reported in more prestigious journal outlets are more likely to be cited by other scholars, even after controlling for various proxies of study quality.

Auto-correlation of journal impact factor for consensus research reporting statements: a cohort study

Background. The Journal Citation Reports journal impact factors (JIFs) are widely used to rank and evaluate journals, standing as a proxy for the relative importance of a journal within its field. However, numerous criticisms have been made of use of a JIF to evaluate importance. This problem is exacerbated when the use of JIFs is extended to evaluate not only the journals, but the papers therein. The purpose of this study was therefore to investigate the relationship between the number of citations and journal IF for identical articles published simultaneously in multiple journals.

Methods. Eligible articles were consensus research reporting statements listed on the EQUATOR Network website that were published simultaneously in three or more journals. The correlation between the citation count for each article and the median journal JIF over the published period, and between the citation count and number of article accesses was calculated for each reporting statement.

Results. Nine research reporting statements were included in this analysis, representing 85 articles published across 58 journals in biomedicine. The number of citations was strongly correlated to the JIF for six of the nine reporting guidelines, with moderate correlation shown for the remaining three guidelines (median r = 0.66, 95% CI [0.45–0.90]). There was also a strong positive correlation between the number of citations and the number of article accesses (median r = 0.71, 95% CI [0.5–0.8]), although the number of data points for this analysis were limited. When adjusted for the individual reporting guidelines, each logarithm unit of JIF predicted a median increase of 0.8 logarithm units of citation counts (95% CI [−0.4–5.2]), and each logarithm unit of article accesses predicted a median increase of 0.1 logarithm units of citation counts (95% CI [−0.9–1.4]). This model explained 26% of the variance in citations (median adjusted r² = 0.26, range 0.18–1.0).

Conclusion. The impact factor of the journal in which a reporting statement was published was shown to influence the number of citations that statement will gather over time. Similarly, the number of article accesses also influenced the number of citations, although to a lesser extent than the impact factor. This demonstrates that citation counts are not purely a reflection of scientific merit and the impact factor is, in fact, auto-correlated.

Why do we think we know what we know? A metaknowledge analysis of the salt controversy

BACKGROUND

Although several public health organizations have recommended population-wide reduction in salt intake, the evidence on the population benefits remains unclear. We conducted a metaknowledge analysis of the literature on salt intake and health outcomes.

METHODS

We identified reports--primary studies, systematic reviews, guidelines and comments, letters or reviews--addressing the effect of sodium intake on cerebro-cardiovascular disease or mortality. We classified reports as supportive or contradictory of the hypothesis that salt reduction leads to population benefits, and constructed a network of citations connecting these reports. We tested for citation bias using an exponential random graph model. We also assessed the inclusion of primary studies in systematic reviews on the topic.

RESULTS

We identified 269 reports (25% primary studies, 5% systematic reviews, 4% guidelines and 66% comments, letters, or reviews) from between 1978 and 2014. Of these, 54% were supportive of the hypothesis, 33% were contradictory and 13% were inconclusive. Reports were 1.51 [95% confidence interval (CI) 1.38 to 1.65] times more likely to cite reports that drew a similar conclusion, than to cite reports drawing a different conclusion. In all, 48 primary studies were selected for inclusion across 10 systematic reviews. If any given primary study was selected by a review, the probability that a further review would also have selected it was 27.0% (95% CI 20.3% to 33.7%).

CONCLUSIONS

We documented a strong polarization of scientific reports on the link between sodium intake and health outcomes, and a pattern of uncertainty in systematic reviews about what should count as evidence.

Citations alone were enough to predict favorable conclusions in reviews of neuraminidase inhibitors

OBJECTIVES

To examine the use of supervised machine learning to identify biases in evidence selection and determine if citation information can predict favorable conclusions in reviews about neuraminidase inhibitors.

STUDY DESIGN AND SETTING

Reviews of neuraminidase inhibitors published during January 2005 to May 2013 were identified by searching PubMed. In a blinded evaluation, the reviews were classified as favorable if investigators agreed that they supported the use of neuraminidase inhibitors for prophylaxis or treatment of influenza. Reference lists were used to identify all unique citations to primary articles. Three classification methods were tested for their ability to predict favorable conclusions using only citation information.

RESULTS

Citations to 4,574 articles were identified in 152 reviews of neuraminidase inhibitors, and 93 (61%) of these reviews were graded as favorable. Primary articles describing drug resistance were among the citations that were underrepresented in favorable reviews. The most accurate classifier predicted favorable conclusions with 96.2% accuracy, using citations to only 24 of 4,574 articles.

CONCLUSION

Favorable conclusions in reviews about neuraminidase inhibitors can be predicted using only information about the articles they cite. The approach highlights how evidence exclusion shapes conclusions in reviews and provides a method to evaluate citation practices in a corpus of reviews.

Association between success rate and citation count of studies of radiofrequency catheter ablation for atrial fibrillation: possible evidence of citation bias

BACKGROUND

The preferential citation of studies with the highest success rates could exaggerate perceived effectiveness, particularly for treatments with widely varying published success rates such as radiofrequency catheter ablation for atrial fibrillation.

METHODS AND RESULTS

We systematically identified observational studies and clinical trials of radiofrequency catheter ablation of atrial fibrillation between 1990 and 2012. Generalized Poisson regression was used to estimate association between study success rate and total citation count, adjusting for sample size, journal impact factor, time since publication, study design, and whether first or last author was a consensus-defined pre-eminent expert. We identified 174 articles meeting our inclusion criteria (36 289 subjects). After adjustment only for time since publication, a 10-point increase above the mean in pooled reported success rates was associated with a 17.8% increase in citation count at 5 years postpublication (95% confidence interval, 7.1-28.4%; P<0.001). After additional adjustment for impact factor, sample size, randomized trial design, and pre-eminent expert authorship, the association remained significant (18.6% increase in citation count; 95% confidence interval, 7.6-29.6%; P<0.0001). In this full model, time since publication, impact factor, and pre-eminent expert authorship were significant covariates, whereas randomized control trial design and study sample size were not.

CONCLUSIONS

Among studies of radiofrequency catheter ablation of atrial fibrillation, high success rate was independently associated with citation count, which may indicate citation bias. To readers of the literature, radiofrequency catheter ablation of atrial fibrillation could be perceived to be more effective than the data supports. These findings may have implications for a wide variety of novel cardiovascular therapies.

A retrospective analysis of dissemination biases in the brief alcohol intervention literature

This study examined dissemination and reporting biases in the brief alcohol intervention literature. We used retrospective data from 179 controlled trials included in a meta-analysis on brief alcohol interventions for adolescents and young adults. We examined whether the magnitude and direction of effect sizes were associated with publication type, identification source, language, funding, time lag between intervention and publication, number of reports, journal impact factor, and subsequent citations. Results indicated that effect sizes were larger for studies that had been funded (b = 0.14, 95% confidence interval [CI] [0.04, 0.23]), had a shorter time lag between intervention and publication (b = -0.03, 95% CI [-0.05, -.001]), and were cited more frequently (b = 0.01, 95% CI [+0.00, 0.01]). Studies that were cited more frequently by other authors also had greater odds of reporting positive effects (odds ratio = 1.10, 95% CI [1.02, 1.18]). Results indicated that time lag bias has increased recently: Larger and positive effect sizes were published more quickly in recent years. We found no evidence, however, that the magnitude or direction of effects was associated with location source, language, or journal impact factor. We conclude that dissemination biases may indeed occur in the social and behavioral science literature, as has been consistently documented in the medical literature. As such, primary researchers, journal reviewers, editors, systematic reviewers, and meta-analysts must be cognizant of the causes and consequences of these biases, and commit to engage in ethical research practices that attempt to minimize them. (PsycINFO Database Record

Quality of reporting of randomized controlled trials published in Intensive Care Medicine from 2001 to 2010

PURPOSE

To evaluate the methodological quality of randomized controlled trials (RCTs) published in Intensive Care Medicine from 2001 to 2010, and to compare it with a previous review of RCTs published from 1975 to 2000.

METHODS

We assessed the quality of reporting of randomization, blinding and participant flow, both individually and combined within the Jadad scale, and compared them with findings from our previous review. For RCTs published from 2001 to 2010, we also evaluated the frequency of distorted finding presentation (spin) and inflated predicted treatment effect (delta inflation).

RESULTS

In the 221 RCTs from 2001 to 2010, the sample size was significantly larger than in the older series, and there was a higher proportion of studies with negative findings. Reporting of the rationale for sample size estimation and allocation concealment increased significantly, but reporting of other important individual methodological components did not change substantially compared with the previous period and remained low. Among RCTs from 2001 to 2010, a spin strategy was used in 69 of 111 RCTs with statistically negative results, while delta inflation was present in 7 of 11 RCTs evaluating survival as a primary outcome. Papers with higher Jadad scores were cited more often than the others.

CONCLUSIONS

Quality of reporting of RCTs published in Intensive Care Medicine has only partly improved over time, and spin and delta bias are of frequent occurrence. There is a need for stronger adherence to CONSORT recommendations, with special emphasis on accurate description of randomization and blindness, and correct reporting of statistically non-significant results.

Citation bias favoring statistically significant studies was present in medical research

OBJECTIVE

Statistically significant studies may be cited more than negative studies on the same topic. We aimed to assess here whether such citation bias is present across the medical literature.

STUDY DESIGN AND SETTING

We conducted a cohort study of the association between statistical significance and citations. We selected all therapeutic intervention studies included in meta-analyses published between January and March 2010 in the Cochrane database, and retrieved citation counts of all individual studies using ISI Web of Knowledge. The association between the statistical significance of each study and the number of citations it received between 2008 and 2010 was assessed in mixed Poisson models.

RESULTS

We identified 89 research questions addressed in 458 eligible articles. Significant studies were cited twice as often as nonsignificant studies (multiplicative effect of significance: 2.14, 95% confidence interval: 1.38-3.33). This association was partly because of the higher impact factor of journals where significant studies are published (adjusted multiplicative effect of significance: 1.14, 95% confidence interval: 0.87-1.51).

CONCLUSION

A citation bias favoring significant results occurs in medical research. As a consequence, treatments may seem more effective to the readers of medical literature than they really are.

The impact of article length on the number of future citations: a bibliometric analysis of general medicine journals

Background

The number of citations received is considered an index of study quality and impact. We aimed to examine the factors associated with the number of citations of published articles, focusing on the article length.

Methods

Original human studies published in the first trimester of 2006 in 5 major General Medicine journals were analyzed with regard to the number of authors and of author-affiliated institutions, title and abstract word count, article length (number of print pages), number of bibliographic references, study design, and 2006 journal impact factor (JIF). A multiple linear regression model was employed to identify the variables independently associated with the number of article citations received through January 2012.

Results

On univariate analysis the JIF, number of authors, article length, study design (interventional/observational and prospective/retrospective), title and abstract word count, number of author-affiliated institutions, and number of references were all associated with the number of citations received. On multivariate analysis with the logarithm of citations as the dependent variable, only article length [regression coefficient: 14.64 (95% confidence intervals: (5.76–23.50)] and JIF [3.37 (1.80–4.948)] independently predicted the number of citations. The variance of citations explained by these parameters was 51.2%.

Conclusion

In a sample of articles published in major General Medicine journals, in addition to journal impact factors, article length and number of authors independently predicted the number of citations. This may reflect a higher complexity level and quality of longer and multi-authored studies.

Magnitude of effects in clinical trials published in high-impact general medical journals

BACKGROUND

Prestigious journals select for publication studies that are considered most important and informative. We aimed to examine whether high-impact general (HIG) medical journals systematically demonstrate more favourable results for experimental interventions compared with the rest of the literature.

METHODS

We scrutinized systematic reviews of the Cochrane Database (Issue 4, 2009) and meta-analyses published in four general journals (2008-09). Eligible articles included ≥1 binary outcome meta-analysis(es) pertaining to effectiveness with ≥1 clinical trial(s) published in NEJM, JAMA or Lancet. Effect sizes in trials from NEJM, JAMA or Lancet were compared with those from other trials in the same meta-analyses by deriving summary relative odds ratios (sRORs). Additional analyses examined separately early- and late-published trials in HIG journals and journal-specific effects.

RESULTS

A total of 79 meta-analyses including 1043 clinical trials were analysed. Trials in HIG journals had similar effects to trials in other journals, when there was large-scale evidence, but showed more favourable results for experimental interventions when they were small. When HIG trials had less than 40 events, the sROR was 1.64 [95% confidence interval (95% CI): 1.23-2.18). The difference was most prominent when small early trials published in HIG journals were compared with subsequent trials [sROR 2.68 (95% CI: 1.33-5.38)]. Late-published HIG trials showed no consistent inflation of effects. The patterns did not differ beyond chance between NEJM, JAMA or Lancet.

CONCLUSIONS

Small trials published in the most prestigious journals show more favourable effects for experimental interventions, and this is most prominent for early-published trials in such journals. No effect inflation is seen for large trials.

A meta-review of evidence on heart failure disease management programs: the challenges of describing and synthesizing evidence on complex interventions

BACKGROUND

Despite favourable results from past meta-analyses, some recent large trials have not found heart failure (HF) disease management programs to be beneficial. To explore reasons for this, we evaluated evidence from existing meta-analyses.

METHODS

Systematic review incorporating meta-review was used. We selected meta-analyses of randomized controlled trials published after 1995 in English that examined the effects of HF disease management programs on key outcomes. Databases searched: MEDLINE, EMBASE, Cochrane Database of Systematic Reviews (CDSR), DARE, NHS EED, NHS HTA, Ageline, AMED, Scopus, Web of Science and CINAHL; cited references, experts and existing reviews were also searched.

RESULTS

15 meta-analyses were identified containing a mean of 18.5 randomized trials of HF interventions +/- 10.1 (range: 6 to 36). Overall quality of the meta-analyses was very mixed (Mean AMSTAR Score = 6.4 +/- 1.9; range 2-9). Reporting inadequacies were widespread around populations, intervention components, settings and characteristics, comparison, and comparator groups. Heterogeneity (statistical, clinical, and methodological) was not taken into account sufficiently when drawing conclusions from pooled analyses.

CONCLUSIONS

Meta-analyses of heart failure disease management programs have promising findings but often fail to report key characteristics of populations, interventions, and comparisons. Existing reviews are of mixed quality and do not adequately take account of program complexity and heterogeneity.

Pharmacotherapy for smoking cessation: current advances and research topics

Promoting smoking cessation is among the key medical interventions aimed at reducing worldwide morbidity and mortality in this century. Both behavioural counselling and pharmacotherapy have been shown to significantly increase long-term abstinence rates, and combining the two treatment modalities is recommended. This article provides an update on pharmacotherapy for smoking cessation in the general population. Current first-line agents used to support quit attempts are nicotine replacement therapy (NRT), bupropion and varenicline. Research suggests that abstinence rates can be increased by combining different forms of NRT or simultaneously administering NRT and non-nicotine medications. New treatments targeting the nicotinic acetylcholine receptor as well as other pathophysiological pathways involved in nicotine addiction are being developed, with nicotine vaccines now being tested in phase III clinical trials. Among the numerous research topics currently addressed, pharmacogenetics and tailoring therapy to specific groups of smokers look most promising. However, substantial progress is unlikely to be made unless social gradients impeding effective treatment of all smokers are overcome. In addition, public smoking bans and reimbursement of medication costs are crucial in reducing the future burden of disease caused by smoking on a global level.

Do pressures to publish increase scientists' bias? An empirical support from US States Data

The growing competition and “publish or perish” culture in academia might conflict with the objectivity and integrity of research, because it forces scientists to produce “publishable” results at all costs. Papers are less likely to be published and to be cited if they report “negative” results (results that fail to support the tested hypothesis). Therefore, if publication pressures increase scientific bias, the frequency of “positive” results in the literature should be higher in the more competitive and “productive” academic environments. This study verified this hypothesis by measuring the frequency of positive results in a large random sample of papers with a corresponding author based in the US. Across all disciplines, papers were more likely to support a tested hypothesis if their corresponding authors were working in states that, according to NSF data, produced more academic papers per capita. The size of this effect increased when controlling for state's per capita R&D expenditure and for study characteristics that previous research showed to correlate with the frequency of positive results, including discipline and methodology. Although the confounding effect of institutions' prestige could not be excluded (researchers in the more productive universities could be the most clever and successful in their experiments), these results support the hypothesis that competitive academic environments increase not only scientists' productivity but also their bias. The same phenomenon might be observed in other countries where academic competition and pressures to publish are high.

Citation analysis of identical consensus statements revealed journal-related bias

OBJECTIVE

To examine whether the prestige of a journal, measured by its impact factor, influences the numbers of citations obtained by published articles, independently of their scientific merit.

STUDY DESIGN AND SETTING

In this cohort study, citation counts were retrieved for articles describing consensus statements that were published in multiple journals and were correlated with the impact factors of the source journals.

RESULTS

Four consensus statements were published in multiple copies: QUOROM (QUality Of Reporting Of Meta-analyses) was published in three journals, CONSORT (CONsolidated Standards Of Reporting Trials) in eight journals, STARD (STAndards for Reporting of Diagnostic accuracy) in 14 journals, and STROBE (STrengthening the Reporting of OBservational studies in Epidemiology) in eight journals. For each consensus statement, the impact factor of the source journal and the number of citations were highly correlated (Spearman correlation coefficients: QUOROM, 1.00; CONSORT, 0.88; STARD, 0.65; and STROBE, 0.81-all P<0.02). When adjusted for time since publication, each logarithm unit of impact factor predicted an increase of 1.0 logarithm unit of citations (95% confidence interval: 0.7-1.3, P<0.001), and the variance explained was 66% (adjusted r(2)=0.66).

CONCLUSIONS

The prominence of the journal where an article is published, measured by its impact factor, influences the number of citations that the article will gather over time. Citation counts are not purely a reflection of scientific merit.