| Year | Value (SE) |
|---|---|
| 2005 | 0.3480 (0.3172) |
| 2006 | 0.9964 (0.1828) |
| 2007 | 0.4388 (0.2753) |
| 2008 | 1.3727 (0.2910) |
| 2009 | 0.8849 (0.0982) |
| 2010 | 0.7601 (0.1446) |
| 2011 | 1.2509 (0.1325) |
| 2012 | 1.0888 (0.1194) |
| 2013 | 0.6982 (0.0942) |
| 2014 | 0.7157 (0.1123) |
| 2016 | 0.8119 (0.0693) |
| 2017 | 0.7972 (0.0757) |
| 2018 | 0.8459 (0.1254) |
| 2019 | 1.1512 (0.1513) |
| 2020 | 1.2310 (0.3887) |
| 2021 | 0.4503 (0.1724) |
| 2022 | 1.0318 (0.5152) |
| 2023 | 0.7607 (0.1816) |
| 2024 | 0.5554 (0.3291) |
