| Year | Value (SE) |
|---|---|
| 2000 | 0.3677 (0.0471) |
| 2001 | 0.4004 (0.0075) |
| 2002 | 0.3899 (0.0138) |
| 2003 | 0.2927 (0.0226) |
| 2004 | 0.2210 (0.0133) |
| 2005 | 0.1906 (0.0075) |
| 2006 | 0.2620 (0.0135) |
| 2007 | 0.3150 (0.0194) |
| 2008 | 0.4192 (0.0227) |
| 2009 | 0.3837 (0.0231) |
| 2010 | 0.4846 (0.0729) |
| 2011 | 0.2875 (0.0176) |
| 2012 | 0.2988 (0.0165) |
| 2013 | 0.2080 (0.0200) |
| 2014 | 0.2546 (0.0195) |
| 2015 | 0.2852 (0.0666) |
| 2016 | 0.3114 (0.0157) |
| 2019 | 0.4085 (0.0409) |
| 2020 | 0.6217 (0.1300) |
| 2021 | 0.9554 (1.0257) |
| 2022 | 0.4240 (0.0854) |
| 2023 | 0.5129 (0.0635) |
