| Year | Value (SE) |
|---|---|
| 2003 | 0.7190 (0.0081) |
| 2007 | 0.4720 (0.0363) |
| 2008 | 0.7890 (0.0168) |
| 2009 | 0.9060 (0.0074) |
| 2010 | 0.8480 (0.0306) |
| 2011 | 0.9260 (0.0076) |
| 2012 | 0.9270 (0.0079) |
| 2013 | 0.8120 (0.0336) |
| 2014 | 0.8540 (0.0283) |
| 2015 | 0.5980 (0.0245) |
| 2018 | 0.8140 (0.0202) |
| 2019 | 0.6450 (0.0179) |
| 2020 | 0.6360 (0.0257) |
| 2021 | 0.4530 (0.0110) |
| 2022 | 0.6260 (0.0231) |
| 2023 | 0.6270 (0.0120) |
