THE fear that a powerful wave of automation might wreak havoc on labour markets has received more serious treatment over the last year (in this newspaper, as elsewhere, than it has in decades). That is thanks in large part to the work of Erik Brynjolfsson and Andrew McAfee, whosebooks have helped legitimise the idea that technological progress is accelerating. But one can also credit technological progress itself; the tech sector has delivered what certainly feels like a striking succession of impressive new technologies over the last few years, from driverless cars, to mind-controlled prosthetics, to scarily powerful machine intelligence.

One chuckles a bit to recall that only 18 months ago the debate was quite a different one, focused on whether the process of economic growth itself might not be in danger thanks to a slowing of discovery. That, in turn, was largely driven by the pessimistic research of economist Robert Gordon, who argued that the pace of growth in real output per person seemed to have been slipping steadily since the peak of the "one great wave" of industrialisation and technological discovery. Rich economies showed little sign of escaping the productivity doldrums into which they sank in the early 1970s; the tech boomlet of the late 1990s and early 2000s came and went all too quickly.

On reviewing the evidence, this newspaper came to a rather more optimistic assessment than Mr Gordon.

Closer analysis of recent figures, though, suggests reason for optimism. Across the economy as a whole productivity did slow in 2005 and 2006—but productivity growth in manufacturing fared better. The global financial crisis and its aftermath make more recent data hard to interpret. As for the strong productivity growth in the late 1990s, it may have been premature to see it as the effect of information technology making all sorts of sectors more productive. It now looks as though it was driven just by the industries actually making the computers, mobile phones and the like. The effects on the productivity of people and companies buying the new technology seem to have begun appearing in the 2000s, but may not yet have come into their own.

In a new NBER working paper, however, John Fernald, of the Federal Reserve Bank of San Francisco, argues that the past decade's data are clear enough. Productivity growth did indeed slow down from around 2005, he finds, returning to a trend rate near the level from 1973 to 1995. The slowdown clearly predates the global recession and seems to have persisted right through it and into recovery. Slower productivity growth does not appear to be related to any unusual activity in the housing or financial sectors; rather, it came in the same sectors that drove the boom from 1996 to 2004: those producing IT or using it intensively.

Is this evidence that Mr Gordon is right and Mssrs Brynjolfsson and McAfee wrong? Not exactly, for reasons that are clear enough in Mr Fernald's work. He writes:

A natural hypothesis is that the slowdown was the flip side of the mid-1990s speedup. Considerable evidence...links the [productivity] speedup to the exceptional contribution of IT—computers, communications equipment, software, and the Internet. IT has had a broad-based and pervasive effect through its role as a general purpose technology (GPT) that fosters complementary innovations, such as business reorganization. Industry...data provide evidence in favor of the IT hypothesis versus alternatives...IT users saw a sizeable bulge in [productivity] growth in the early 2000s, even as IT spending itself slowed. That pattern is consistent with the view that benefiting from IT takes substantial intangible organizational investments that, with a lag, raise measured productivity. By the mid-2000s, the low-hanging fruit of IT had been plucked.

Let's break this down a bit. IT driven productivity growth came first to the sectors producing IT equipment, related to things like advanced in semiconductor technologies. But IT is what economists call a "general purpose technology", which means that it can be applied and used to boost productivity across many sectors. Achieving those gains requires investment, however, in equipment but also in "intangible capital": in a nutshell, figuring out what to do with the stuff and how to reorganise the business to use it most effectively. By the early 2000s, the nature of the productivity boom had shifted, from IT industries themselves to sectors that found ways to use IT intensively. And as Mr Fernald says, the easy gains from IT had been realised by mid-decade.

But that should immediately set at least some alarm bells ringing. Mid-decade, in this story, was the middle of last decade, or ten years ago. A lot has changed since then. Or as we wrote back in 2013:

Research by Susanto Basu of Boston College and John Fernald of the San Francisco Federal Reserve suggests that the lag between investments in information-and-communication technologies and improvements in productivity is between five and 15 years. The drop in productivity in 2004, on that reckoning, reflected a state of technology definitely pre-Google, and quite possibly pre-web.

Stories about disruption from accelerating technological progress really can't be tested in any sensible way against available productivity data. It's been within the last few years that smartphones with 3G connections achieved greater than 50% market penetration in rich countries, for instance. Firms are still fumbling around trying to figure out what that sort of thing allows them to do. Business models enabled by the web, like new approaches to online higher education, are only now becoming sophisticated enough to influence the market. And the really impressive new technologies, like autonomous vehicles and powerful machine intelligence, are scarcely beyond the realm of experimental prototype.

It seems difficult to believe that such dramatic new machines could become part of the fabric of the modern economy without generating massive economic change, including faster productivity growth. Yet one has to allow that this is, to some extent, a matter of faith, at least for the moment. We can observe the technology and compare it to what came before. And we can observe the frenetic efforts to bring new products and businesses to market. But then we have to bide our time. Indeed, the more potentially transformative the technology, the longer it may take for business—and society, for that matter—to learn to maximise its economic benefits.

So we continue to wait, and wonder.