| Year | Value (SE) |
|---|---|
| 2000 | 0.6840 (0.0109) |
| 2001 | 0.7470 (0.0033) |
| 2002 | 0.6670 (0.0119) |
| 2003 | 0.7140 (0.0118) |
| 2004 | 0.6290 (0.0046) |
| 2005 | 0.5340 (0.0041) |
| 2006 | 0.6360 (0.0108) |
| 2007 | 0.6820 (0.0105) |
| 2008 | 0.6940 (0.0082) |
| 2009 | 0.6980 (0.0090) |
| 2010 | 0.6810 (0.0249) |
| 2011 | 0.5720 (0.0086) |
| 2012 | 0.6950 (0.0105) |
| 2013 | 0.7190 (0.0245) |
| 2014 | 0.6880 (0.0114) |
| 2015 | 0.6560 (0.0348) |
| 2016 | 0.7120 (0.0067) |
| 2019 | 0.6260 (0.0244) |
| 2020 | 0.6180 (0.0204) |
| 2021 | 0.7590 (0.0261) |
| 2022 | 0.6450 (0.0246) |
| 2023 | 0.5540 (0.0094) |
