| 2008 | 2009 | 2010 | 2011 | 2012 | 2013 | 2014 | 2015 | 2016 | 2017 |
| 3.3 × 10−4 | 3.0 × 10−4 | 2.2 × 10−4 | 1.8 × 10−4 | 1.2 × 10−4 | 1.2 × 10−4 | 1.2 × 10−4 | 8.9 × 10−5 | 7.7 × 10−5 | 7.3 × 10−5 |
| 3.0 × 10−3 | 2.8 × 10−3 | 2.2 × 10−3 | 2.0 × 10−3 | 1.5 × 10−3 | 1.6 × 10−3 | 1.5 × 10−3 | 1.3 × 10−3 | 1.0 × 10−3 | 0.9 × 10−3 |
| 4.5 × 10−2 | 4.0 × 10−2 | 3.1 × 10−2 | 2.9 × 10−2 | 1.9 × 10−2 | 2.0 × 10−2 | 1.8 × 10−2 | 1.5 × 10−2 | 1.4 × 10−2 | 1.4 × 10−2 |