AERS spider: an online interactive tool to mine statistical associations in Adverse Event Reporting System.
Grigoriev I, zu Castell W, Tsvetkov P, Antonov AV. Pharmacoepidemiol Drug Saf. 2014 Aug;23(8):795-801.

Background Set

In many cases it is more natural to use not the entire report population as background but reports from a more specific large subpopulation where the prior risk of the Adverse Outcome is more adequately modeled. For example, to explore the risk of fracture in relation to "calcium" administration one need either to select as background "OSTEOPOROSIS" reports or to use all reports excluding the indications with "Bone Density" problems.