What will decide the US election and why it's so close

Never in recent US political history has the outcome of a presidential been so in doubt - this is not a contest for the faint of heart.

While past elections have been narrowly decided - George W Bush's 2000 victory over Al Gore came down to a few hundred votes in Florida - there's always been some sense of which direction the race was tilting in the final days.

Sometimes, as in 2016, the sense is wrong. In that year, polls overestimated Hillary Clinton's strength and failed to detect a late-breaking movement in Donald's Trump favour.

This time around, however, the arrows are all pointing in different directions. No-one can seriously make a prediction either way.