| Year | Value (SE) |
|---|---|
| 2008 | 0.7690 (0.0340) |
| 2009 | 0.8260 (0.0135) |
| 2010 | 0.8160 (0.0406) |
| 2011 | 0.8130 (0.0134) |
| 2012 | 0.8030 (0.0119) |
| 2013 | 0.7870 (0.0276) |
| 2014 | 0.8970 (0.0253) |
| 2015 | 1.0670 (0.1217) |
| 2016 | 0.7630 (0.0159) |
| 2018 | 0.7870 (0.0240) |
| 2019 | 0.9390 (0.0601) |
| 2020 | 0.8130 (0.0303) |
| 2022 | 0.7520 (0.0176) |
| 2023 | 0.7660 (0.0187) |
