Stocks keep going up. It can't continue – or can it? Investors could be forgiven for seeing recent strength as unsustainable. Being up by more than 10 per cent by April means the S&P 500 is in "rare air", says LPL Research's Ryan Detrick, who notes the index managed to hit 21 new highs in less than 70 trading days this year.

Indeed, it gained 54 per cent in the 12 months to the end of March – one of the largest-ever yearly gains.

Technically overbought conditions can sometimes spell short-term trouble. Looking at previous 12-month periods where stocks gained at least 35 per cent, Detrick found returns were mixed over the following one-, three- and six-month periods.

However, history suggests any trouble will be fleeting. One year later, the S&P 500 was higher more than 90 per cent of the time, enjoying median returns of 14.9 per cent.

Detrick’s take: “We wouldn’t bet on this bull market ending anytime soon”.