Butler said that AA "looks like it couldn't survive as there's no leadership or top-level telling local cumanns what to do, but it has worked and proved itself extremely robust". Butler explained that "AA's 'inverted pyramid' style of governance has helped it to avoid many of the pitfalls that political and religious institutions have encountered since it was established here in 1946." In 2018, AA counted 2,087,840 members and 120,300 AA groups worldwide. The Twelve Traditions informally guide how individual AA groups function, and the Twelve Concepts for World Service guide how the organization is structured globally. A member who accepts a service position or an organizing role is a "trusted servant" with terms rotating and limited, typically lasting three months to two years and determined by group vote and the nature of the position. Each group is a self-governing entity with AA World Services acting only in an advisory capacity. AA is served entirely by alcoholics, except for seven "nonalcoholic friends of the fellowship" of the 21-member AA Board of Trustees. AA groups are self-supporting, relying on voluntary donations from members to cover expenses. The AA General Service Office (GSO) limits contributions to US$3,000 a year. Above the group level, AA may hire outside professionals for services that require specialized expertise or full-time responsibilities. Like individual groups, the GSO is self-supporting. AA receives proceeds from books and literature that constitute more than 50% of the income for its General Service Office. In keeping with AA's Seventh Tradition, the Central Office is fully self-supporting through the sale of literature and related products, and the voluntary donations of AA members and groups. It does not accept donations from people or organizations outside of AA. In keeping with AA's Eighth Tradition, the Central Office employs special workers who are compensated financially for their services, but their services do not include traditional "12th Step" work of working with alcoholics in need. All 12th Step calls that come to the Central Office are handed to sober AA members who have volunteered to handle these calls. It also maintains service centers, which coordinate activities such as printing literature, responding to public inquiries, and organizing conferences. Other International General Service Offices (Australia, Costa Rica, Russia, etc.) are independent of AA World Services in New York. Program AA's program extends beyond abstaining from alcohol. Its goal is to effect enough change in the alcoholic's thinking "to bring