Unpublished abstracts can be invaluable

We read with great interest the paper by Al-Qaoud and colleagues¹ and letter by Hoag.² Hoag stated that “the next time you go to a medical meeting, bring a coin — you’re going to have to flip it to decide whether to believe what you hear or not.” This means that the quality of a medical congress can be assessed by the number of journal papers arising from the presentations.² We would like to point out that this statement is one side of the coin. There are many factors that affect the publication of meeting abstracts. These factors are not related to the quality of research presented in meetings. One of these important factors is publication bias. It is well-documented that an important factor predicting publication after presentation of a study at a scientific meeting is a positive outcome of study.³ Some studies reported that papers with non-significant or negative results are substantially less likely to be submitted for publication.⁴ This tendency to publish research based on the strength and direction of results defined as “publication bias.”⁵ Consequently, some high quality studies do not publish based on their negative results. This failure to publish influences the information available for analysis and decision making by the scientific communities. Of course, if some research is left unpublished for their negative or non-significant results, there is less information available for systematic reviews and guidelines. So, the entire unpublished studies do not suffer from poor quality and this biased information may result in poor validity of systematic reviews’ conclusions and guidelines. In some instances, conference abstracts can be an important source for systematic reviews and failure to identify studies presented in congresses might threaten the validity of systematic reviews and clinical guidelines.⁶