NO ABSTRACT AVAILABLE (NAA) BIAS:
A bias relevant to studies of knowledge synthesis (e.g. systematic reviews), that occurs when new data or information is omitted from a review study because the article, within which the new data or information is contained, does not have an abstract available in the electronic database that is used for screening1,2.
When an abstract for a paper is not available (e.g. in the case of research letters or editorials), the paper may be viewed as less attractive, and/or less important to scientists conducting reviews, and therefore may be passed over and excluded. In some cases these papers may be reported as unobtainable, in a review study.
Exclusion of papers without abstracts may introduce a Publication Bias in a review, if the papers contain new data or information that should be considered in a meta-analysis. No Abstract Available (NAA) Bias threatens a review study in a similar way to Grey Literature Bias, and may be prevented by ensuring all relevant papers are eligible for inclusion in a review; whether they have an abstract or not. Also see: Grey Literature Bias, Full Text On The Net (FUTON) Bias, Language Bias, and Publication Bias.
References:
1. Wentz R. Visibility of research: FUTON bias. Lancet. 2002;360(9341):1256. (Link to Reference)
2. Murali NS, Murali HR, Auethavekiat P, Erwin PJ, Mandrekar JN, Manek NJ, et al. Impact of FUTON and NAA bias on visibility of research. Mayo Clin Proc. 2004;79(8):1001-6. (Link to Reference)