* The metric is PPP Per worked hour. I don't think PPP is a great measurement of productivity. There are many factors that impact PPP that have nothing to do with productivity.
* In the US we work more hours. We defiantly work so many hours that we are past the diminishing returns of peak productivity hours. Here on HN we sometimes debate if our workers overall productivity would increase if we lowered the amount of working hours.
* Growth is a weird factor in economies. It's easy to grow when you aren't at the top. Smaller economies can reach 8% growth by importing techniques and technology from more advanced economies. The most advanced economies usually grow at about 2% because they have to invent the new stuff to be more productive.
* The US' population is much more diverse than European countries. Our geographic, cultural, and ethic diversity creates unique challenges and not all of our boats are rising equally. I think it's likely we are leaving a subsection of our population behind economically and this is showing up in the population numbers. Of course this is a serious problem, but it doesn't necessarily indicate the median US worker should be worried about a European taking their job.