| Year | Value (SE) |
|---|---|
| 2008 | 0.8200 (0.0838) |
| 2009 | 1.0230 (0.0337) |
| 2010 | 1.0220 (0.0566) |
| 2011 | 0.9930 (0.0269) |
| 2012 | 0.9420 (0.0237) |
| 2013 | 1.0440 (0.0834) |
| 2014 | 1.0020 (0.0522) |
| 2015 | 1.1670 (0.1109) |
| 2016 | 1.0150 (0.0256) |
| 2017 | 0.9960 (0.0330) |
| 2019 | 1.0020 (0.0690) |
| 2020 | 1.0250 (0.0996) |
| 2021 | 1.1940 (0.3103) |
