Young JM, Solomon MJ (February 2009). According to the conflict of interest policy conflicts of interest (COI) must be disclosed. Avoid over-emphasizing single studies, particularly in vitro or animal studies edit In vitro studies and animal models serve a central role in research, and are invaluable in determining mechanistic pathways and generating hypotheses. These methods are often best when writing about oneself, one's organization or company but may be less so when there is a potential conflict of interest in a research field. Some systematic reviews also include a statistical meta-analysis to combine the results of several clinical trials to provide stronger quantitative evidence about how well a treatment works for a particular purpose. Rosmarakis ES, Soteriades ES, Vergidis PI, Kasiakou SK, Falagas ME (May 2005). Primary sources may be presented together with secondary sources. Journal of the Medical Library Association.