| Year | Value (SE) |
|---|---|
| 2008 | 0.7399 (0.0516) |
| 2009 | 0.8491 (0.0311) |
| 2010 | 0.6567 (0.1280) |
| 2011 | 0.7619 (0.0135) |
| 2013 | 0.6074 (0.0877) |
| 2014 | 0.8191 (0.1019) |
| 2015 | 0.5398 (0.2131) |
| 2016 | 0.8075 (0.0572) |
| 2017 | 0.7415 (0.0332) |
| 2018 | 0.8305 (0.0752) |
| 2019 | 0.8662 (0.0813) |
| 2020 | 1.3543 (0.6661) |
| 2021 | 0.7905 (0.2941) |
| 2023 | 0.8572 (0.2102) |
| 2024 | 0.4354 (0.1735) |
