As defined by the constitution of 1926 and subsequent amendments, Lebanon is an independent republic. Executive power is vested in a president (elected by the legislature for six years) and a prime minister and cabinet, chosen by the president but responsible to the legislature. Under an agreement dating back to the French mandate, the president must be a Maronite Christian, the prime minister a Sunni Muslim, and the president of the National Assembly a Shi'a Muslim. Decisions by the president must be countersigned by the prime minister and concerned minister (s) after approval by the National Assembly. Legislative power is exercised by a 128-member National Assembly (formerly the Chamber of Deputies), elected for a four-year term by universal adult suffrage (compulsory for males of twenty-one or over, permitted for women over twenty-one with elementary education). The electoral reform law of 1960 determined the denominational composition of the legislature as follows: thirty Maronites; twenty Sunni, nineteen Shi'a; eleven Greek Orthodox; six Greek Catholics; six Druzes; four Armenian Orthodox; one Armenian Catholic; one Protestant; and one Others. Deputies were elected to the legislature in 1972, but elections scheduled for 1976 were postponed because of the war, and the legislature has extended its term every two years until 1992. The Taif Accord of 1989 set the Christian-Muslim balance in parliament at fifty-fifty, but the failure of Christians to participate in the elections of 1992 and 1996 gave Muslim groups the largest number of seats in the Chamber. There has been no official census in the country since 1932, but most observers believe Muslims now form the majority with the Shi'i as the largest single group. The denominational composition of the legislature following the 2000 elections was: Maronites (34), Sunnites (27), Shi'ites (27), Greek Orthodox (14), Greek Catholics (8), Druzes (8), Armenian Orthodox (5), Alaouites (2), Armenian Catholics (1), Protestants (1), and Christian Minorities (1).