| Year | United States | China |
| 2010 | 2.60% | 10.60% |
| 2011 | 1.60% | 9.50% |
| 2012 | 2.20% | 7.90% |
| 2013 | 1.80% | 7.80% |
| 2014 | 2.50% | 7.30% |
| 2015 | 2.90% | 6.90% |
| 2016 | 1.60% | 6.70% |
| 2017 | 2.20% | 6.80% |
| 2018 | 2.90% | 6.60% |