| Year | Value (SE) |
|---|---|
| 2008 | 1.0075 (0.2042) |
| 2009 | 0.7827 (0.0752) |
| 2010 | 0.7443 (0.0878) |
| 2011 | 0.8857 (0.0961) |
| 2012 | 0.8017 (0.0766) |
| 2013 | 0.6521 (0.0732) |
| 2014 | 0.6336 (0.0787) |
| 2015 | 0.5000 (0.0914) |
| 2016 | 0.6772 (0.0632) |
| 2017 | 0.6573 (0.0725) |
| 2018 | 0.7184 (0.0944) |
| 2019 | 1.0437 (0.1308) |
| 2020 | 1.0427 (0.2547) |
| 2021 | 0.8007 (0.2816) |
| 2022 | 0.7339 (0.2678) |
| 2023 | 0.6440 (0.1204) |
| 2024 | 0.7599 (0.3812) |
