Equities run out of steam

No sooner had stock markets climbed back to record or multi-year highs late last week than they had another US-induced attack of vertigo. Technology stocks led the sell-off, with America's tech-heavy Nasdaq index losing almost 5% in three days. The world's 14 biggest internet companies have now lost 20% of their value in little more than a month.

The S&P 500 slipped into the red for the year early this week. Britain's FTSE 100 suffered its worst day in a month on Monday. Three UK e-commerce stocks, recently-listed Just Eat and AO World, plus Asos, fell by 6%-14% in two days.

What the commentators said

But tech bubble 2.0' isn't the only factor spoiling investors' risk appetite. China's slowdown, the increasingly tense stand-off in eastern Ukraine, and the US Federal Reserve's ongoing tapering aren't helping. Earnings forecasts have fallen, with S&P 500 first-quarter earnings expected to come in 3% below last year's tally.

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At the start of the year, 2% profit growth was expected. A rapid jump is unlikely any time soon. A key problem is that profit margins are already at a record high, leaving sales growth to power profits, and the US and global economy are only recovering gradually.

In cyclically adjusted terms (which takes a longer view of earnings), it is more than 50% overvalued compared to the long-term average.

Be afraid, said Lahart. Market sell-offs typically have an identifiable trigger, such as the release of a lousy piece of economic data. "Share prices crumbling just because prices have reached a point where investors can no longer stomach them can signal real trouble."

When the big bear market began in March 2000, after the first tech bubble burst, there was "no compelling cause".