| Year | Value (SE) |
|---|---|
| 2006 | 0.9310 (0.0927) |
| 2007 | 0.8720 (0.1223) |
| 2008 | 0.9550 (0.1315) |
| 2009 | 0.7360 (0.0699) |
| 2010 | 0.8760 (0.1338) |
| 2011 | 0.8740 (0.0812) |
| 2012 | 1.0580 (0.0552) |
| 2013 | 0.8290 (0.0753) |
| 2014 | 1.0850 (0.1083) |
| 2015 | 0.7910 (0.1671) |
| 2016 | 0.7820 (0.0567) |
| 2017 | 0.9250 (0.1008) |
| 2018 | 0.8220 (0.0922) |
| 2019 | 1.0180 (0.2510) |
| 2020 | 0.8110 (0.2418) |
| 2021 | 0.5760 (0.3912) |
| 2022 | 1.2420 (0.4938) |
| 2023 | 0.6100 (0.1120) |
| 2024 | 1.4630 (0.6887) |
