Misconceptions surrounding the relationship between journal impact factor and citation distribution in veterinary medicine

Citation inequality and the Journal Impact Factor: median, mean, (does it) matter?

Skewed citation distribution is a major limitation of the Journal Impact Factor (JIF) representing an outlier-sensitive mean citation value per journal The present study focuses primarily on this phenomenon in the medical literature by investigating a total of n = 982 journals from two medical categories of the Journal Citation Report (JCR). In addition, the three highest-ranking journals from each JCR category were included in order to extend the analyses to non-medical journals. For the journals in these cohorts, the citation data (2018) of articles published in 2016 and 2017 classified as citable items (CI) were analysed using various descriptive approaches including e.g. the skewness, the Gini coefficient, and, the percentage of CI contributing 50% or 90% of the journal’s citations. All of these measures clearly indicated an unequal, skewed distribution with highly-cited articles as outliers. The %CI contributing 50% or 90% of the journal’s citations was in agreement with previously published studies with median values of 13–18% CI or 44–60% CI generating 50 or 90% of the journal’s citations, respectively. Replacing the mean citation values (corresponding to the JIF) with the median to represent the central tendency of the citation distributions resulted in markedly lower numerical values ranging from − 30 to − 50%. Up to 39% of journals showed a median citation number of zero in one medical journal category. For the two medical cohorts, median-based journal ranking was similar to mean-based ranking although the number of possible rank positions was reduced to 13. Correlation of mean citations with the measures of citation inequality indicated that the unequal distribution of citations per journal is more prominent and, thus, relevant for journals with lower citation rates. By using various indicators in parallel and the hitherto probably largest journal sample, the present study provides comprehensive up-to-date results on the prevalence, extent and consequences of citation inequality across medical and all-category journals listed in the JCR.

Incomplete reporting of experimental studies and items associated with risk of bias in veterinary research

In in vivo research, the reporting of core items of study design is persistently poor, limiting assessment of study quality and study reproducibility. This observational cohort study evaluated reporting levels in the veterinary literature across a range of species, journals and research fields. Four items (randomisation, sample size estimation, blinding and data exclusion) were assessed as well as availability of study data in publicly accessible repositories. From five general and five subject-specific journals, 120 consecutively published papers (12 per journal) describing in vivo experimental studies were selected. Item reporting was scored using a published scale (items ranked as fully, partially or not reported) according to completeness of reporting. Papers in subject-specific journals had higher median reporting levels (50.0 per cent vs 33.3 per cent, P=0.007). In subject-specific journals, randomisation (75.0 per cent vs 41.7 per cent, P=0.0002) and sample size estimation (35.0 per cent vs 16.7 per cent, P=0.025) reporting was approximately double that of general journals. Blinding (general 48.3 per cent, subject-specific 50.0 per cent, P=0.86) and data exclusion (general 53.3 per cent, subject-specific 63.3 per cent, P=0.27) were similarly reported. A single paper made study data readily accessible. Incomplete reporting remains prevalent in the veterinary literature irrespective of journal type, research subject or species. This impedes evaluation of study quality and reproducibility, raising concerns regarding wasted financial and animal resources.