Key factors in the Wentworth by-election

KEY FACTORS IN WENTWORTH BY-ELECTION:

* Coalition government has trailed in 40-plus Newspolls in a row.

* Member for Wentworth, Malcolm Turnbull, who held the seat with a 17.75 per cent margin, was dumped as prime minister without explanation and declined to play a role in the campaign to replace himself.

* Independent Kerryn Phelps has a strong local profile as a GP, media commentator, health advocate and outspoken campaigner for marriage equality.

* By-elections on average swing against governments by about five percentage points.

* Voters are well aware not electing Liberal candidate Dave Sharma will put the coalition into minority in the parliament, sending a strong wake-up call ahead of an election due by May 2019.

* Prime Minister Scott Morrison is still on training-wheels and his colleagues are watching him closely as he seeks to put the coalition on an election-winning footing.

* Some MPs in the Nationals party room believe the coalition does not have a clear direction and could turn on leader Michael McCormack if there are signs the wheels are falling off the government.