I really don't like August. It's nothing about the weather, or the fact that the kids are really ready to be back in school (but aren't). I just really can't stand the monkey business. August is, after December, probably the month in which liquidity is the thinnest; in a world with thousands of hedge funds this means that if there is any new information the market tends to have dramatic swings. More to the point, it means that if there is not any new information, the speculators make their own swings. A case in point today was the massive 5% rally in energy futures from their lows of the day back to the recent highs. There was no news of note - the IEA said that demand will balance the oil market later this year, but they have said that in each of the last couple of months too. And the move was linear, as if there had been news.

Don't get me wrong, I don't care if traders monkey around with prices in the short run. They can't change the underlying supply and demand imbalance and so it's just noise trading for noise trading's sake. What bothers me is that I have to take time out of my day to go and try to find out whether there is news that I should know. And that's annoying.

But my whining is not the main reason for this column today. I am overdue to write about some of the inflation-related developments that bear comment. I'll address one of them today. (Next week, I will probably tackle another - but Tuesday is also CPI day, so I'll post my usual tweet summary. Incidentally, I'm scheduled to be on What Did You Miss? on Bloomberg TV at 4pm ET on Tuesday - check your local listings).

I don't spend a lot of time worrying about productivity (other than my own, and that of my employees). We are so bad at measuring productivity that the official data are revised for many years after their release. For example, the "productivity miracle" of the late 1990s, which drove the Internet bubble and the equity boom into the end of the century, was eventually revised away almost completely. It never happened.

The problem that a lot of people have with thinking about productivity is that they confuse the level of productivity with its pace of increase. So someone will say "of course the Internet changed everything and we got more productive," when the real question is whether the pace of productivity increase accelerated. We are always getting more productive over time. There are always new innovations. What we need to know is whether those innovations and cost savings are happening more quickly than they used to, or more slowly. And, since the national accounts are exquisitely bad at picking up new forms of economic activity, and at measuring things like intellectual property development, it is always almost impossible to reject in real time the hypothesis that "nothing is changing about the rate of productivity growth." Therefore, I don't spend much time worrying about it.

But, that being said, we should realize that if there is a change in the rate of productivity growth it has implications for growth, but also for inflation. And recent productivity numbers, combined with the a priori predictions in some quarters that the global economy is entering a slow-productivity phase, have started to draw attention.

Most of that attention is focused on the fact that poor productivity growth lowers overall real output. The mechanism there is straightforward: productivity growth plus population growth equals real economic output growth. (Technically, more than just population growth it is working-age population growth times labor force participation, but the point is that it's an increase in the number of workers, compounded by the increase in each worker's productivity, that increases real output). Especially if a populist backlash in the US against immigration causes labor force growth to slow, a slower rate of productivity growth would compound the problem of how to grow real economic growth at anything like the rate necessary to support equity markets or, for that matter, the national debt.

But there hasn't been as much focus on the other problem of low productivity growth, if indeed we are entering into that sort of era. The other problem is that low productivity growth causes higher prices, all else equal. That mechanism is also straightforward. We know that money growth plus the change in money velocity equals real output growth plus an increase in prices: that is, MV?PQ. If velocity is mean-reverting, then the decline in real growth precipitated by a decline in labor productivity, in the context of an unchanged rate of increase in the money supply, implies higher prices. That is, if DM is constant and DV is zero and DQ declines, then DP must increase.

One partial offset to this is the fact that a permanent decline in productivity growth rates would lower the equilibrium real interest rate, which would lower the equilibrium money velocity. But that is a one-time shift while the change in trend output would be lasting.

In fact, it wouldn't be unreasonable to suppose that the change in interest rates we have seen in the last few years is mostly cyclical but may also be partly secular. This would imply a lower equilibrium level of interest rates (although I don't mean to imply that anything is near equilibrium these days), and a lower equilibrium level of monetary velocity. But there are a lot of "ifs" in that statement.

The biggest "if" of all, of course, is whether there really is a permanent or semi-permanent down-shift in long-term productivity growth. I don't have a strong opinion on that, although I suspect it's more likely true that the current angst over low productivity growth rates is just the flip side of the 1990s ebullience about productivity. We'll know for sure…in about a decade.

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