Introduction: The source of scientific information, methods for their evaluation, and methodology of their use are critical for serious scientific research and publishing of the scientific research results. Certain methodological principles should be inexcusably followed when designing clinical or observational research to avoid bias and presentation of results that do not reflect the truth about the phenomenon that is the object of the study. Aim: The aim of this study was to compare the methodological quality of clinical trials and observational studies published in medical journals from ex-Yugoslav countries indexed in Web of Science (WoS) and Pubmed/MEDLINE. Methods: Clinical studies published in medical journals of ex-Yugoslav countries were retrieved from the WoS and Pubmed database, and the sample for analysis was randomly chosen from the retrieved publications. The rate of the most common errors in the design of clinical/observational studies was established by a careful reading of the sampled publications and their checking against predefined criteria. Results: Number and percent of the evaluated studies that failed to meet each of the methodological criteria tested, number of the evaluated criteria not satisfied per database and number of studies that satisfied more than 4 criteria were analyzed per database. When explanatory potential of journal impact factor, number of citations, time elapsed from publication and a database where a journal is referred were tested by linear regression in regard to the number of methodological criteria satisfied per study, the linear regression model was obtained by backward deletion method and achieved R2 adjusted of 0.166 (F=13.827, df1 = 2, df2 = 127, p=0.000). The methodological quality of studies was directly related to impact factor of the journals (B = 0.976, 95% confidence interval 0.539 1.413, p=0.000) and inversely with the database where a journal is referred (B =0.444, 95% confidence interval0.824 -0.064, p = 0.022). Each additional unit of impact factor increased number of satisfied methodological criteria for about 1, while referring a journal only in WoS decreased number of satisfied criteria for 0.45 points in comparison with journals referred in both WoS and Pubmed/MEDLINE, and for 0.9 points in comparison to journals referred only in MEDLINE.. Conclusion: Methodological and scientometric quality of clinical studies published in medical journals from ex-Yugoslav region varies significantly, and the variations are higher in journals referenced only in WoS than in journals referenced in Pubmed/MEDLINE only, or in both Pubmed and Web of Science databases..
Key words: Methodological errors, Clinical studies, Research design, Statistical errors.
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