| Year | Value (SE) |
|---|---|
| 2008 | 1.0220 (0.1490) |
| 2009 | 1.0800 (0.0903) |
| 2010 | 1.0400 (0.1710) |
| 2011 | 0.8630 (0.0367) |
| 2012 | 0.9340 (0.0370) |
| 2013 | 1.2210 (0.1135) |
| 2014 | 1.1490 (0.1185) |
| 2015 | 0.9870 (0.1848) |
| 2016 | 0.9400 (0.0797) |
| 2018 | 0.8950 (0.1123) |
| 2019 | 1.0890 (0.0941) |
| 2020 | 0.7540 (0.2708) |
| 2022 | 0.8290 (0.2547) |
| 2023 | 0.9940 (0.1557) |
| 2025 | 0.4730 (0.2245) |
