I recently berated Greg Mankiw (and the top ten world economists he pretends top cite) for the folly of suggesting that fertility rates don’t matter to economists. Well today Mankiw seems to be having (an implicit) rethink. Dependency ratios, it seems, do matter.
Now since dependency ratios are really a function of three factors – fertility, life expectancy and net migration – it is hard to deny the obvious: that fertility is important.
Mankiw also cites approvingly the opinion of US economist Jeremy Siegel to the effect that the “way to finance the baby boomers’ retirement is persistent capital inflows and trade deficits with developing countries”. Now Siegel doesn’t quite have this right here. The way to finance a high old-age dependency ratio, is through a high level of saving, and running persistent capital *outflows* and trade *surpluses*. This, of course, is precisely what Germany and Japan are now doing, (and also, incidentally, steering the currency down to reduce deflationary pressure, which is again what has been happening in Japan) and this is one of the reasons I give so much importance to this phenomenon. It is also one of the reasons why I discount the likelihood of domestic-demand-driven growth in these countries.
So all I can say is, well, well, well, welcome onboard Greg. As is well known both time consistency and cognitive dissonance are phenomena which constitute important problems for economic theory, but normally not in the sense that we can see them at work here.
A topic whose time has finally come? We will see. To quote the evolutionary biologist Linda Partridge (in another context) “there is much to do”. Would that economists were as aware of this as theoretical biologists seem to be.
Update: the problem is more perplexing than I initially imagined, since I now discover that on July 20th Greg approvingly cites a paper by Nir Jaimovich and Henry Siu. The title of the paper is The Young, the Old, and the Restless: Demographics and Business Cycle Volatility , and the extract he cites is this one:
“changes in the age composition of the labor force account for a significant fraction of the variation in business cycle volatility observed in the US and other G7 economies“.
Greg says that this was the most intriguing hypothesis he had heard all day (he was at the NBER Summer Institute), which is fair enough, and I don’t expect him to agree with the hypothesis simply because he finds it intriguing, but I *am* stumped to understand how he can then go on on August 26 to describe the idea that low fertility posed a serious economic problem as one of the most wrong headed ideas he had heard recently, since, obviously, it is fertility levels which in part determine age structures which in part influence volatility in business cycles (according to the intriguing hypothesis). So come on Greg, which is it, wrong-headed or intriguing?
Seriously though, my point here is not to have a go at Greg Mankiw (although I have rather done that haven’t I?). My point is to draw attention to all the confusion which is knocking about on this topic. Material not unrelated to all of this is to be found in a recent article in the FT by John Kay. Kay asks hijmself why it is that Eureka moments seldom happen to economists. Basically he suggests that the reason is down to the difference between the natural and the social sciences. I don’t buy that, and I think that we social scientists sell ourselves too cheap if we succumb to it. But by the by Kay touches on another point, and it is one which brings us back to the struggle Greg Mankiw is having with the recalcitrant phenomena, since:
“It will rarely, if ever, be the case in economics that an old account of the world will be shown to be simply wrong, like the medieval account of planetary motion, or the phlogiston theory of heat.”
Well sorry John, but we have just found one that is: the neo classical account of steady state growth, there is no real factual basis for this theory, and theoretically it isn’t hard to see that it must be flawed, if, that is, the ‘intriguing hypothesis’ which Greg was scratching his head about is a valid one, and thus, since age structures constantly change, so must rates of economic growth. In which case both steady state growth and convergence theory go quietly west, off into the sunset. The intriguing question is then of course what exactly it is which modulates the changes in age structure. This is, of course, just the kind of problem that Archimedes was toiling away with in the relatively unturbulent waters of his bathtub. Aha, now I know why it is economists seldom have Eureka moments: they all take showers.
Now just let me step outside a moment, what is going on out there, is that the sun going round the earth, or could it just be that somehow or another the earth – unbeknownst to me – is actually turning round the sun.