Country development and publication bias: a review of published studies

Reza Yousefi Nooraie, Soroush Mortaz Hejri

Background:

Publication bias is the selective publication of manuscripts based on the magnitude, direction, or statistical significance of the study results. Another reason may be a substantial editorial bias against the researches from less-developed countries
Objectives:

To compare the methodological quality and statistical appeal of trials from countries with different developmental status and to determine their association with the journal impact factors and the language of publication in articles cited in Medline and Embase.
Methods:

Selection criteria: Based on the World Bank income criteria, countries were divided into four groups. All records of clinical trials conducted in each income group during 1993 and 2003 were included if the abstract and sample size were mentioned. Search strategy:

Cochrane Controlled Trials Register was searched and 50 articles selected from each income group using a systematic random sampling method in years 1993 and 2003 separately. Data extraction: Data were extracted by two reviewers on the language of publication, use of randomization, blinding, intention to treat analysis, sample size, statistical significance and containing an obvious conclusion. Disagreement was dealt with by consensus. Journal impact factors were obtained from the institute for scientific information.
Results:

Four hundred records were explored. Country income had an inverse linear association with the presence of randomization (chi2 for trend=4.82, p=0.02) and a direct association with the use of blinding (chi2 for trend=6.9, p=0.008); although in low income countries the probability of blinding was increased from 36% in 1993 to 53.5% in 2003. In 1993 the results of 68% of high income trials and 64.7% of other groups were statistically significant; but in 2003 they were 66% and 88% respectively. Sample size and income were the only significant predictors of journal impact factor. The use of randomization, blinding and reporting significant results were more likely in English articles and these differences were more noticeable in 2003.
Conclusion:

The impact of country development on publication bias is increasing with time. It seems that the guidelines for improving the reporting quality of trials have been more strictly implemented for developing world researchers.

Melbourne 2005 O-35

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