Box 1Definitions of some types of reporting biases^a

Publication bias

The publication or nonpublication of research because of the nature and direction of the results.

Time lag bias

The rapid or delayed publication of research because of the nature and direction of the results.

Multiple publication bias

The multiple or singular publication of research because of the nature and direction of the results.

Location bias

The publication of research in journals with different ease of access or levels of indexing in standard databases because of the nature and direction of results.

Citation bias

The citation or noncitation of research because of the nature and direction of the results.

Language bias

The publication of research in a particular language because of the nature and direction of the results.

Outcome reporting bias

The selective reporting, in published studies, of one or more outcomes because of the nature and direction of the results.

Analysis reporting bias

The selective reporting, in published studies, of one or more analyses as a change from planned analyses or as a selection from two or more analysis options because of the nature and direction of the results.

a

Adapted from definitions provided in the Cochrane Handbook for Systematic Reviews of Interventions.¹⁹