| Year | Value (SE) |
|---|---|
| 2006 | 0.7225 (0.1145) |
| 2007 | 0.8955 (0.1413) |
| 2008 | 0.7917 (0.1635) |
| 2009 | 0.5476 (0.0897) |
| 2010 | 0.6509 (0.1191) |
| 2011 | 0.5541 (0.0918) |
| 2012 | 0.8242 (0.0691) |
| 2013 | 0.7287 (0.1004) |
| 2014 | 1.0676 (0.1777) |
| 2015 | 0.5830 (0.1699) |
| 2016 | 0.7335 (0.0945) |
| 2017 | 0.8047 (0.1133) |
| 2018 | 0.6642 (0.1039) |
| 2019 | 1.5524 (0.6402) |
| 2020 | 0.7275 (0.2354) |
| 2021 | 0.5662 (0.3990) |
| 2022 | 1.1724 (0.5977) |
| 2023 | 0.5826 (0.1291) |
| 2024 | 1.0431 (0.5641) |
