| Year | Value (SE) |
|---|---|
| 2008 | 0.4081 (0.0229) |
| 2009 | 0.4913 (0.0125) |
| 2010 | 0.3202 (0.0242) |
| 2011 | 0.4547 (0.0070) |
| 2012 | 0.5531 (0.0081) |
| 2013 | 0.6076 (0.0245) |
| 2014 | 0.7726 (0.0156) |
| 2015 | 0.6971 (0.0702) |
| 2016 | 0.7944 (0.0238) |
| 2017 | 0.6988 (0.0241) |
| 2018 | 0.6284 (0.0316) |
| 2019 | 0.2717 (0.0185) |
| 2020 | 0.4848 (0.0609) |
| 2021 | 0.4831 (0.3250) |
| 2022 | 0.3322 (0.0403) |
