| Year | Value (SE) |
|---|---|
| 2008 | 1.0012 (0.3034) |
| 2009 | 0.9534 (0.2180) |
| 2010 | 0.7715 (0.1936) |
| 2011 | 1.1880 (0.1685) |
| 2012 | 0.9043 (0.1296) |
| 2013 | 1.0917 (0.2409) |
| 2014 | 0.7386 (0.1585) |
| 2015 | 0.4949 (0.1364) |
| 2016 | 0.5539 (0.0902) |
| 2018 | 0.6513 (0.1992) |
| 2019 | 0.7940 (0.2570) |
| 2020 | 1.0694 (0.6820) |
| 2022 | 0.5809 (0.3132) |
| 2023 | 0.7942 (0.3002) |
