Determinants of citation in the literature on diesel exhaust exposure and lung cancer: a citation analysis

Bram Duyx, Miriam J E Urlings, Gerard M H Swaen, Lex M Bouter, Maurice P Zeegers

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OBJECTIVES: Epidemiological research on the association between diesel exhaust exposure and lung cancer risk has some methodological challenges that give rise to different conclusions and intense debates. This raises the question about the role of selective citation and of citation bias in particular. Our aim was to investigate the occurrence and prevalence of selective citation in this field.

DESIGN: Citation analysis.

SETTING: Web of Science Core Collection.

PARTICIPANTS: We identified 96 publications in this network, with 4317 potential citations. For each publication, we extracted characteristics such as study conclusion and funding source. Some of these characteristics are related to the study content: study design, sample size, method of diesel exposure assessment, type of diesel technology under investigation, and whether smoking had been adjusted for.

PRIMARY AND SECONDARY OUTCOME MEASURES: Whether a citation occurs or not, measured and analysed according to the preregistered protocol. Exploratively we analysed the association between funding source and study conclusion.

RESULTS: Methodological content of a study was clearly related to citation, studies using more sophisticated methods were more likely to be cited. There was some evidence for citation bias: supportive publications had a higher chance of being cited than non-supportive ones, but after adjustment for study quality, this effect decreased substantially (adjusted OR 1.3, 95% CI 1.0 to 1.7). Explorative analyses indicated that three quarters of non-profit funded publications had a supportive study conclusion against only one quarter of the industry-funded publications.

CONCLUSIONS: There is evidence for selective citation within this field, but the evidence for citation bias was weak. It seems that factors related to the methodology had more impact on citation than the conclusion of a study. Interestingly, publications that were funded by industry were more skeptical about a causal relationship between diesel exhaust and lung cancer compared to non-profit-funded publications.

Original languageEnglish
Article number033967
Pages (from-to)e033967
JournalBMJ Open
Issue number10
Publication statusPublished - 7 Oct 2020

Bibliographical note

© Author(s) (or their employer(s)) 2020. Re-use permitted under CC BY-NC. No commercial re-use. See rights and permissions. Published by BMJ.


χ2(2)=9.2, p=0.01. Non-supportive conclusion includes publications that concluded no association or an unclear association. Seven publications (six exclusively non-profit and one with combined funding) did not state a clear conclusion and were excluded from these analyses, as were the two (exclusively non-profit) publications that had reached a mixed conclusion. Publications that failed to report their funding source were also excluded. Three of the for-profit publications were funded by financial institutions, all the other ones by the transport industry. Only one of the publications funded by the transport industry had reached a supportive conclusion.

FundersFunder number
Long-Range Research Initiative
European Chemical Industry CouncilLRI-Q3-UM


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