| Year | Value (SE) |
|---|---|
| 2008 | 0.6680 (0.1636) |
| 2009 | 0.7611 (0.1139) |
| 2010 | 0.8036 (0.1076) |
| 2011 | 1.0200 (0.1509) |
| 2012 | 0.7944 (0.1190) |
| 2013 | 0.8265 (0.1767) |
| 2014 | 1.1012 (0.2314) |
| 2015 | 0.5745 (0.1605) |
| 2016 | 0.8979 (0.0883) |
| 2017 | 0.8721 (0.1360) |
| 2019 | 0.7960 (0.3303) |
| 2020 | 1.2611 (0.4832) |
| 2021 | 0.2686 (0.2687) |
