How rare is it for a prime minister to attract 4 floor-crossers in 4 months?

Floor-crossing has always been a feature of Canadian politics dating back to the first Parliament — and seeing four opposition MPs jump ship to join the government in a matter of months is rare but not unprecedented.

Prime Minister Mark Carney has only been in office for a year and is ranking near the top in terms of prime ministers who have had opposition MPs join his caucus during a parliamentary session.

John A. Macdonald, Robert Borden and Jean Chrétien attracted a swath of MPs to their respective governments — though all in vastly different circumstances.

Using information from the Library of Parliament, CBC News compiled a list of MPs who have changed political affiliation to join a governing caucus since Confederation. MPs who left politics to return and run under a different party and MPs who left a governing caucus in protest only to rejoin later were excluded.

Macdonald holds the distinction for welcoming the most MPs into his government during a session. Nine opposition members crossed the floor to sit in Canada's first prime minister's caucus — five of whom crossed on the same day in 1869.

But Macdonald benefited from unique circumstances that don't neatly compare to Carney's situation.

Every floor-crosser that joined Macdonald's government came from the Anti-Confederation Party — a coalition of MPs mostly from the East Coast that sought to undo the formation of the Dominion of Canada.

That party collapsed during the first Parliament and its MPs largely dispersed between Macdonald's Conservatives and the Liberals. Anti-Confederation Leader Joseph Howe himself joined the governing caucus in April 1969.

Robert Borden, who served as prime minister during the First World War, got a total of 17 MPs to join his ranks — though only one crossed the floor in the middle of a parliamentary session.

Sixteen sitting Liberal MPs ran and were elected with Borden's Unionist government in the 1917 election which was almost exclusively contested on the conscription issue.

Borden and his pro-conscription slate won — but after the war, several MPs returned to the Liberals while others stayed with the Conservatives.

Chrétien is a more modern equivalent to Carney's current context, though not perfectly comparable.

During his decade in office, eight MPs from the opposition benches joined Chrétien's government.

Like Carney, Chrétien also attracted MPs from multiple parties, including: the NDP, the Progressive Conservatives, the Bloc Québécois and even the Canadian Alliance (formerly the Reform Party).