| Year | Value (SE) |
|---|---|
| 2005 | 0.7720 (0.0087) |
| 2006 | 0.7540 (0.0135) |
| 2007 | 0.7180 (0.0723) |
| 2008 | 0.8330 (0.0304) |
| 2009 | 0.8030 (0.0085) |
| 2010 | 0.8230 (0.0372) |
| 2011 | 0.7610 (0.0094) |
| 2012 | 0.8030 (0.0097) |
| 2013 | 0.7770 (0.0235) |
| 2014 | 0.7890 (0.0182) |
| 2016 | 0.8290 (0.0098) |
| 2017 | 0.8110 (0.0117) |
| 2018 | 0.8080 (0.0109) |
| 2019 | 0.7810 (0.0118) |
| 2020 | 0.7590 (0.0141) |
| 2021 | 0.7200 (0.0091) |
| 2022 | 0.7160 (0.0140) |
| 2023 | 0.7670 (0.0125) |
| 2024 | 0.7270 (0.0232) |
