For more than a decade, the economy’s rate of productivity growth has been dismal, which is bad news for workers since their incomes rise slowly or not at all when this is the case. Economists have struggled to understand why American productivity has been so weak. After all, with all the information technology innovations that make our lives easier like iPhones, Google goog , and Uber, why hasn’t our country been able to work more productively, giving us either more leisure time, or allowed us to get more done at work and paid more in return?

One answer often given is that the government statisticians must be measuring something wrong – notably, the benefits of Google and all the free stuff we can now access on our phones, tablets and computers. Perhaps government statisticians just couldn’t figure out how to include those new services in a meaningful way into the data?

A new research paper by Fed economists throws cold water on that idea. They think that free stuff like Facebook fb should not be counted in GDP, or in measures of productivity, because consumers do not pay for these services directly; the costs of providing them are paid for by advertisers. The authors point out that free services paid for by advertising are not new; for example, when television broadcasting was introduced it was provided free to households and much of it still is.

The Fed economists argue that free services like Google are a form of “consumer surplus,” defined as the value consumers place on the things they buy that is over and above the price they have paid. Consumer surplus has never been included in past measures of GDP or productivity, they point out. Economist Robert Gordon, who commented on the Fed paper at the conference where it was presented, argued that even if consumer surplus were to be counted, most of the free stuff such as search engines, e-commerce, airport check-in kiosks and the like was already available by 2004, and hence would not explain the productivity growth slowdown that occurred around that time.

The Fed economists also point out that the slowdown in productivity growth is a very big deal. If the rate of growth achieved from 1995 to 2004 had continued for another decade, GDP would have been $3 trillion higher, the authors calculate. And the United States is not alone in facing weak productivity; it is a problem for all developed economies. It is hard to believe that such a large problem faced by so many countries could be explained by errors in the way GDP and productivity are measured.

Even though I agree with the Fed authors that the growth slowdown is real, there are potentially serious measurement problems for the economy that predate the 2004 slowdown.

Health care is the most important example. It amounts to around 19% of GDP and in the official accounts there has been no productivity growth at all in this sector over many, many years. In part that may reflect inefficiencies in health care delivery, but no one can doubt that the quality of care has increased. New diagnostic and scanning technologies, new surgical procedures, and new drugs have transformed how patients are treated and yet none of these advances has been counted in measured productivity data. The pace of medical progress probably was just as fast in the past as it is now, so this measurement problem does not explain the slowdown. Nevertheless, trying to obtain better measures of health care productivity is an urgent task. The fault is not with the government’s statisticians, who do a tremendous job with very limited resources. The fault lies with those in Congress who undervalue good economic statistics.

Gordon, in his influential new book The Rise and Fall of American Growth, argues that the American engine of innovation has largely run its course. The big and important innovations are behind us and future productivity growth will be slow. My own view is that the digital revolution has not nearly reached an end, and advances in materials science and biotechnology promise important innovations to come. Productivity growth seems to go in waves and is impossible to forecast, so it is hard to say for sure if Gordon is wrong, but I think he is.

Fortune reported in June 2015 that 70% of its top 500 CEOs listed rapid technological change as their biggest challenge. I am confident that companies will figure out the technology challenge, and productivity growth will get back on track, hopefully sooner rather than later.

Martin Neil Baily is a Senior Fellow in Economic Studies at the Brookings Institution.