Remember back at the beginning of February when the stock markets were all crashing? Feels like ages ago now, I know. Anyway, Seth Ackerman and I had an interesting conversation about it over at Jacobin.
My rather boring view is that short-term movements in stock markets can’t be explained by any kind of objective factors, because in the short run prices are dominated by conventional expectations — investors’ beliefs about investors’ beliefs…  But over longer periods, the value of shares is going to depend on the fraction of output claimed as profits and that, in general, is going to move inversely with the share claimed as wages. So if working people are getting raises — and they are, at least more than they were in 2010-2014 — then shareholders are right to worry about their own claim on the product.
One thing I say in the interview that a couple people have been surprised at, is that
there has been an upturn in business investment. In the corporate sector, at least, business investment, after being very weak for a number of years, is now near the high end of its historical range as a fraction of output.
Really, near the high end? Isn’t investment supposed to be weak?
As with a lot of things, whether investment is weak or strong depends on exactly what you measure. The figure below shows investment as a share of total output for the economy as a whole and for the nonfinancial corporate sector since 1960. The dotted lines show the 10th and 90th percentiles.
As you can see, while invesment for the economy as a whole is near the low end of its historic range, nonfinancial corporate investment is indeed near the high end.
What explains the difference? First, investment by households collapsed during the recession and has not significantly recovered since. This includes purchases of new houses but also improvements of owner-occupied houses, and brokers’ fees and other transactions costs of home sales (that last item accounts for as much as a quarter of residential investment historically; many people don’t realize it’s counted at all). Second, the investment rate of noncorporate businesses is about half what it was in the 1970s and 80s. This second factor is exacerbated by the increased weight of noncorporate businesses relative to corproate businesses over the past 20 years. I’m not sure what concrete developments are being described by these last two changes, but mechanically, they explain a big part of the divergence in the figure above. Finally, the secular increase in the share of output produced by the public sector obviously implies a decline in the share of private investment in GDP.
I think that for the issues Seth and I were talking about, the corporate sector is the most relevant. It’s only there that we can more or less directly observe quantities corresponding to our concepts of “the economy.” In the public (and nonprofit) sector we can’t observe output, in the noncorproate sector we can’t observe profits and wages (they’re mixed up in proprietors income), and in the household sector we can’t observe either. And financial sector has its own issues.
Anyway, you should read the interview, it’s much more interesting than this digression. I just thought it was worth explaining that one line, which otherwise might provoke doubts.
 While this is a truism, it’s worth thinking through under what conditions this kind of random walk behavior applies. The asset needs to be and liquid and long-lived relative to the relevant investment horizon, and price changes over the investment horizon have to be much larger than income or holding costs. An asset that is normally held to maturity is never going to have these sort of price dynamics.