| Year | Value (SE) |
|---|---|
| 2008 | 1.0433 (0.2443) |
| 2009 | 0.8136 (0.0791) |
| 2010 | 0.8389 (0.0994) |
| 2011 | 0.7240 (0.0600) |
| 2012 | 0.8930 (0.0932) |
| 2013 | 0.8187 (0.1315) |
| 2014 | 0.8901 (0.1419) |
| 2015 | 0.6342 (0.1675) |
| 2016 | 0.9666 (0.0665) |
| 2017 | 0.9053 (0.1232) |
| 2019 | 1.2462 (0.4243) |
| 2020 | 0.8988 (0.3124) |
| 2021 | 0.9683 (0.9861) |
