The convincing evidence for the presence of reporting biases, described in Section 10.2, demonstrates the need to search comprehensively for studies that meet the eligibility criteria for a Cochrane review. Review authors should ensure that multiple sources are searched; for example, a search of MEDLINE alone would not be considered sufficient. Sources and methods for searching are described in detail in Chapter 6. Comprehensive searches do not necessarily remove bias, however. Review authors should bear in mind, for example, that study reports may selectively present results; that reference lists may selectively cite sources; and that duplicate publication of results can be difficult to spot. Furthermore, the availability of study information may be subject to time-lag bias, particularly in fast-moving research areas. We now discuss two further means of reducing, or potentially avoiding, reporting biases: the inclusion of unpublished studies, and the use of trial registries.