Over at Equitable Growth: Thomas Piketty emails:
We do provide long run series on capital depreciation in the "Capital Is Back" paper with Gabriel [Zucman] (see http://piketty.pse.ens.fr/capitalisback, appendix country tables US.8, JP.8, etc.). The series are imperfect and incomplete, but they show that in pretty much every country capital depreciation has risen from 5-8% of GDP in the 19th century and early 20th century to 10-13% of GDP in the late 20th and early 21st centuries, i.e. from about 1%[/year] of capital stock to about 2%[/year].
Of course there are huge variations across industries and across assets, and depreciation rates could be a lot higher in some sectors. Same thing for capital intensity.
The problem with taking away the housing sector (a particularly capital-intensive sector) from the aggregate capital stock is that once you start to do that it's not clear where to stop (e.g., energy is another capital intensive sector). So we prefer to start from an aggregate macro perspective (including housing). Here it is clear that 10% or 5% depreciation rates do not make sense.
No, James Hamilton, it is not the case that the fact that "rates of 10-20%[/year] are quite common for most forms of producers’ machinery and equipment" means that 10%/year is a reasonable depreciation rate for the economy as a whole--and especially not for Piketty's concept of wealth, which is much broader than simply produced means of production.
No, Pers Krusell and Anthony Smith, the fact that "[you] conducted a quick survey among macroeconomists at the London School of Economics, where Tony and I happen to be right now, and the average answer was 7%[/year" for "the" depreciation rate does not mean that you have any business using a 10%/year economy-wide depreciation rate in trying to assess how the net savings share would respond to increases in Piketty's wealth-to-annual-net-income ratio.
Who are these London School of Economics economists who think that 7%/year is a reasonable depreciation rate for a wealth concept that attains a pre-World War I level of 7 times a year's net national income? I cannot imagine any of the LSE economists signing on to the claim that back before WWI capital consumption in northwest European economies was equal to 50% of net income--that depreciation was a third of gross economic product...