A 6-step procedure was used for the systematic review and article-selection phases of this project: (1) disease case definition; (2) computer-assisted search for systematic reviews and existing meta-analyses; (3) decision about causality; (4) decision about whether a new meta-analysis is necessary; (5) selection of individual articles, including hand searches, for conducting new meta-analyses; (6) extraction of information about dose-response relationships from existing or new meta-analyses.
