| Year | Value (SE) |
|---|---|
| 2003 | 0.8890 (0.0383) |
| 2007 | 0.7520 (0.1411) |
| 2008 | 0.8780 (0.0276) |
| 2009 | 0.9250 (0.0402) |
| 2010 | 1.0340 (0.1046) |
| 2011 | 0.9340 (0.0222) |
| 2012 | 0.9490 (0.0268) |
| 2013 | 0.7550 (0.0689) |
| 2014 | 0.8920 (0.0752) |
| 2015 | 0.7560 (0.1264) |
| 2018 | 0.8730 (0.0440) |
| 2019 | 0.9350 (0.0729) |
| 2020 | 0.8380 (0.2482) |
| 2021 | 0.4320 (0.1537) |
| 2022 | 0.8060 (0.0850) |
| 2023 | 1.0160 (0.1528) |
