European bourses have this summer loosened the shackles that have traditionally bound their fortunes to those of the US market.

Euro-zone equities have clearly outstripped Wall Street during its shaky last two months, leaving investors to ponder whether the link across the Atlantic is as firm as it used to be.

That debate turns on the issue of what has driven Europe's superior performance. While it has much to do with relative expectations of economic growth, some strategists point also to the effect of takeovers and restructuring among euro-zone companies.

Whatever the reasons, Europe has defied the conventional wisdom that it falls along with the US and then some more. Between July 16th and the end of last week, the Eurotop 300 index came off just 3.8 per cent, against a 5.9 per cent decline in the S&P 500.

ING Barings says the correlation between shifts in European and US equities has fallen by a quarter since the start of the year. This could turn into a trend, suggests the broker, as Europe's economic output moves closer to that of the US.