Many high-profile investors, including Warren Buffett and Howard Marks, have recently expressed caution regarding the prospects for stocks. Two more billionaires, David Tepper and Stanley Druckenmiller, went further last week, bluntly warning that indices look particularly precarious right now. Stocks sold off last Wednesday after Tepper, who has averaged annualised returns of 26 per cent over the last 25 years, warned this was "the second-most overvalued stock market I've even seen" (the 1999 technology bubble occupies top spot).

Druckenmiller, a former trading partner of George Soros, was similarly negative, saying the risk-reward for stocks "is maybe as bad as I've seen it in my career". Certainly, valuations leave little room for disappointment. The S&P 500 trades on 20.4 times estimated earnings, according to FactSet – the highest in 18 years and well above its five-, 10-, 15- and 20-year averages.

The median S&P 500 stock would have to almost halve to trade down to the average valuation seen at the last three bear market bottoms, according to a recent Leuthold Group note, while valuations are 30-40 per cent higher “than seen at even the comparatively-shallow market low of 2002”.

Of course, all valuation metrics have their imperfections, but it’s hard to argue with Tepper when he says the US market “is by anybody’s standard pretty full”.