| Year | Value (SE) |
|---|---|
| 2008 | 1.2510 (0.2470) |
| 2009 | 0.9460 (0.0545) |
| 2010 | 0.9490 (0.0952) |
| 2011 | 0.9390 (0.0481) |
| 2012 | 0.9510 (0.0395) |
| 2013 | 0.9410 (0.1079) |
| 2014 | 1.0290 (0.1223) |
| 2015 | 0.8820 (0.2204) |
| 2016 | 0.8860 (0.0359) |
| 2017 | 0.9530 (0.0573) |
| 2019 | 1.0490 (0.1054) |
| 2020 | 1.2380 (0.3128) |
| 2021 | 2.3000 (2.2708) |
