| Year | Value (SE) |
|---|---|
| 2003 | 0.5689 (0.0252) |
| 2007 | 0.2921 (0.0594) |
| 2008 | 0.5985 (0.0227) |
| 2009 | 0.7280 (0.0348) |
| 2010 | 0.6554 (0.0193) |
| 2011 | 0.8011 (0.0311) |
| 2012 | 0.7300 (0.0325) |
| 2013 | 0.6137 (0.0615) |
| 2014 | 0.6970 (0.0633) |
| 2015 | 0.4263 (0.0730) |
| 2018 | 0.6694 (0.0375) |
| 2019 | 0.5560 (0.0459) |
| 2020 | 0.4493 (0.1332) |
| 2021 | 0.2571 (0.0913) |
| 2022 | 0.5056 (0.0663) |
| 2023 | 0.5982 (0.0902) |
