However, in Labor ministries generally, and the Nationalist Lefroy Ministry (1917–1919), Cabinet's composition is chosen by caucus (a meeting of all Parliamentary members of the party) rather than by the Premier.
The Ministry must command the support of the Legislative Assembly—if it either loses a vote of no confidence on the floor of the Assembly, or loses a general election and hence a majority in the Assembly, it is expected to resign and the Opposition Leader, as prospective Premier, is then expected to form a Ministry.
[citation needed] This means that when a Government loses an election, the Ministry remains in office (in "caretaker mode") until a new Ministry is presented to the Governor for appointment.
For example, when the state election on 6 September 2008 produced a defeat for the Labor government, the Labor ministers remained in office until 23 September 2008, when Premier Colin Barnett appointed a new Ministry.
Until 1948, it was necessary for Ministers, when appointed, to resign their seat in Parliament and re-contest it at a ministerial by-election—these were generally uneventful, but on two occasions, Ministers were defeated—in 1901 when half the Morgans Ministry were defeated, and in 1917 when John Scaddan was defeated upon his appointment to the Lefroy Ministry.