This group’s formal name is the Religious Society of Friends, but Quakers can be used in all references. Members typically refer to themselves as Friends. Historically, Quakers are considered Christian; some Quakers today consider themselves nontheistic. Their worship and business gatherings are called meetings. Although there is no recognized ranking of clergy over lay people, meeting officers are called elders or ministers, and these terms should be capitalized when used before a name. Many Quaker ministers in the Midwest and West use the Rev. before their names.
REFERENCE: Religion Stylebook