As with IPD meta-analyses (see Chapter 18, Section 18.2.1) most PMA are carried out and published by collaborative groups. The collaborative group should include representatives from each of the participating trials and will usually have a steering group or Secretariat who manages the project on a day-to-day basis. The collaborative group may choose to create small, ad hoc groups to address specific issues as they arise, and to provide advice to the steering group or Secretariat on clinical, technical or other issues that may impact on the project.