| Year | Value (SE) |
|---|---|
| 2002 | 0.8080 (0.0198) |
| 2007 | 0.9400 (0.0455) |
| 2008 | 0.8800 (0.0214) |
| 2009 | 0.9650 (0.0268) |
| 2010 | 0.9120 (0.0157) |
| 2011 | 1.0190 (0.0253) |
| 2012 | 0.8930 (0.0147) |
| 2013 | 1.0070 (0.0493) |
| 2014 | 1.0100 (0.0465) |
| 2015 | 0.8750 (0.0794) |
| 2018 | 0.9360 (0.0342) |
| 2019 | 0.7910 (0.0396) |
| 2020 | 0.9430 (0.1484) |
| 2021 | 0.8600 (0.1656) |
| 2022 | 0.8440 (0.0456) |
| 2023 | 0.7950 (0.0545) |
| 2024 | 0.8930 (0.1173) |
