DeLong rises to defend Ben Bernanke, against claims that unconventional monetary policy in recent years has discouraged businesses from investing. Business investment is doing just fine, he says:
As I see it, the Fed’s open-market operations have produced more spending–hence higher capacity utilization–and lower interest rates–has more advantageous costs of finance–and we are supposed to believe that its policies “have hurt business investment”?!?! … As I have said before and say again, weakness in overall investment is 100% due to weakness in housing investment. Is there an argument here that QE has reduced housing investment? No. Is nonresidential fixed investment below where one would expect it to be given that the overall recovery has been disappointing and capacity utilization is not high?
As evidence, DeLong points to the fact that nonresidential investment as a share of GDP is back where it was at the last two business cycle peaks.
As it happens, I agree with DeLong that it’s hard to make a convincing case that unconventional monetary policy is holding back business investment. Arguments about the awfulness of low interest rates seem more political or ideological, based on the real or imagined interests of interest-receivers than any identifiable economic analysis. But there’s a danger of overselling the opposite case.
It is certainly true that, as a share of potential GDP, nonresidential investment is not low by historical standards. But is this the right measure to be looking at? I think not, for a couple of reasons, one relatively minor and one major. The minor reason is that the recent redefinition of investment by the BEA to include various IP spending makes historical comparisons problematic. If we define investment as the BEA did until 2013, and as businesses still do under GAAP accounting standards, the investment share of GDP remains quite low compared to previous expansions. The major reason is that it’s misleading to evaluate investment relative to (actual or potential GDP), since weak investment will itself lead to slower GDP growth. 
On the first point: In 2013, the BEA redefined investment to include a variety of IP-related spending, including the commercial development of movies, books, music, etc. as well as research and development. We can debate whether, conceptually, Sony making Steve Jobs is the same kind of thing as Steve Jobs and his crew making the iPhone. But it’s important to realize that the apparent strength of investment spending in recent expansions is more about the former kind of activity than the latter.  More relevant for present purposes, since this kind of spending was not counted as investment — or even broken out separately, in many cases — prior to 2013, the older data are contemporary imputations. We should be skeptical of comparing today’s investment-cum-IP-and-R&D to the levels of 10 or 20 years ago, since 10 or 20 years ago it wasn’t even being measured. This means that historical comparisons are considerably more treacherous than usual. And if you count just traditional (GAAP) investment, or even traditional investment plus R&D, then investment has not, in fact, returned to its 2007 share of GDP, and remains well below long-run average levels. 
More importantly, using potential GDP as the yardstick is misleading because potential GDP is calculated simply as a trend of actual GDP, with a heavier weight on more recent observations. By construction, it is impossible for actual GDP to remain below potential for an extended period. So the fact that the current recovery is weak by historical standards automatically pulls down potential GDP, and makes the relative performance of investment look good.
We usually think that investment spending the single most important factor in business-cycle fluctuations. If weak investment growth results in a lower overall level of economic activity, investment as a share of GDP will look higher. Conversely, an investment boom that leads to rapid growth of the economy may not show up as an especially high investment share of GDP. So to get a clear sense of the performance of business investment, its better to look at the real growth of investment spending over a full business cycle, measured in inflation-adjusted dollars, not in percent of GDP. And when we do this, we see that the investment performance of the most recent cycle is the weakest on record — even using the BEA’s newer, more generous definition of investment.
The figure above shows the cumulative change in real investment spending since the previous business-cycle peak, using the current (broad) BEA definition. The next figure shows the same thing, but for the older, narrower GAAP definition. Data for both figures is taken from the aggregates published by the BEA, so it includes closely held corporations as well as publicly-traded ones. As the figures show, the most recent cycle is a clear outlier, both for the depth and duration of the fall in investment during the downturn itself, and even more for the slowness of the subsequent recovery.
Even using the BEA’s more generous definition, it took over 5 years for inflation-adjusted investment spending to recover its previous peak. (By the narrower GAAP definition, it took six years.) Five years after the average postwar business cycle peak, BEA investment spending had already risen 20 percent in real terms. As of the second quarter of 2015 — seven-and-a-half years after the most recent peak, and six years into the recovery — broad investment spending was up only 10 percent from its previous peak. (GAAP investment spending was up just 8.5 percent.) In the four previous postwar recoveries that lasted this long, real investment spending was up 63, 24, 56, and 21 percent respectively. So the current cycle has had less than half the investment growth of the weakest previous cycle. And it’s worth noting that the next two weakest investment performances of the ten postwar cycles came in the 1980s and the 2000s. In recent years, only the tech-boom period of the 1990s has matched the consistent investment growth of the 1950s, 1960s and 1970s.
So I don’t think it’s time to hang the “Mission Accomplished” banner up on Maiden Lane quite yet.
As DeLong says, it’s not surprising that business investment is weak given how far output is below trend. But the whole point of monetary policy is to stabilize output. For monetary policy to work, it needs to able to reliably offset lower than normal spending in other areas with stronger than normal investment spending. If after six years of extraordinarily stimulative monetary policy (and extraordinarily high corporate profits), business investment is just “where one would expect given that the overall recovery has been disappointing,” that’s a sign of failure, not success.
 Another minor issue, which I can’t discuss now, is DeLong’s choice to compare “real” (inflation-adjusted) spending to “real” GDP, rather than the more usual ratio of nominal values. Since the price index for investment goods consistent rises more slowly than the index for GDP as a whole, this makes current investment spending look higher relative to past investment spending.
 This IP spending is not generally counted as investment in the GAAP accounting rules followed by private businesses. As I’ve mentioned before, it’s problematic that national accounts diverge from private accounts this way. It seems to be part of a troubling trend of national accounts being colonized by economic theory.
 R&D spending is at least reported in financial statements, though I’m not sure how consistently. But with the other new types of IP investment — which account for the majority of it — the BEA has invented a category that doesn’t exist in business accounts at all. So the historical numbers must involve more than usual amount degree of guesswork.