It may be better not to say, for fear of jinxing it, but even before the recession ends, thoughts are turning to recovery. What kind of upturn can we expect when this is over — vigorous or insipid?

And, just as we are being programmed to expect really serious swine flu in the autumn, how big is the danger of a second wave of recession, the dreaded double-dip?

That the worst of the recession is over, a year after it began, is becoming the consensus, though the Bank of England, announcing an extension of its quantitative easing programme from £75 billion to £125 billion on Thursday, clearly believes that “promising signs that the pace of decline has begun to moderate” need further nurturing.

The monthly purchasing managers’ surveys, produced by Markit for the Chartered Institute of Purchasing & Supply, get less attention than much official data, but are closely watched by economists. The latest tells us that the three main sectors of the economy — manufacturing, construction and services — saw the worst of their declines between November and February. For services, the earliest to perk up, the index tells us that the sector is within a whisker of a return to growth.

One of the interesting questions raised by these surveys is whether the current picture painted by the official statisticians is too bleak. Economists at Goldman Sachs think so, and expect the very weak gross domestic product reading for the first quarter, when there was a drop of 1.9%, to be revised up significantly.

There is a general point here. Bloodcurdling comparisons being made between the current recession and its predecessors, on the basis of the statistics now and in earlier episodes, are so badly flawed as to be almost useless. That will not stop people making them, and it probably will not stop me making them, but let me explain why.

Official statistics get revised, and they usually get revised higher. In late 1998 and early 1999 we appeared to be on the brink of the first recession of the New Labour era, with GDP first flat then down by 0.1%. Revised data now show the economy grew strongly then, up more than 1% in one quarter, and did not even flirt with recession.

Statistical revisions do not make recessions disappear, and there is no way this will be anything other than a bad year, which could retain its title as the worst in the post-war era. But it will look different in time. In March 1992, Norman Lamont had to admit Britain had suffered a 2.5% GDP decline in 1991. Current data show the fall was much less than that, 1.4%. Something similar happened in the early 1980s.

This is one to watch. Of rather more interest is the recovery. The National Institute of Economic and Social Research (NIESR), in its latest quarterly review, concurs with Alistair Darling that the economy will show year-on-year growth in 2010. But it thinks it will be weak, 0.9%, followed by a tentative 2.3% growth rate in 2011.

On that basis, it will take until the spring of 2012 to get back to where we were in the first quarter of 2008, before the recession began. The period between the Beijing and London Olympics will have been lost years for the economy.

It could be worse. Washington’s Peterson Institute last month brought together two former International Monetary Fund chief economists, Michael Mussa and Simon Johnson, to debate global recovery.

Johnson said the world faced an L-shaped “recovery”, the sharp downswing being followed by no upturn in 2010 and not much of one after that.

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