| Year | Value (SE) |
|---|---|
| 2000 | 0.5376 (0.0445) |
| 2001 | 0.4925 (0.0052) |
| 2002 | 0.3845 (0.0106) |
| 2003 | 0.3392 (0.0148) |
| 2004 | 0.2402 (0.0052) |
| 2005 | 0.2181 (0.0041) |
| 2006 | 0.2803 (0.0088) |
| 2007 | 0.3172 (0.0125) |
| 2008 | 0.4154 (0.0122) |
| 2009 | 0.3693 (0.0116) |
| 2010 | 0.3920 (0.0284) |
| 2011 | 0.2799 (0.0110) |
| 2012 | 0.3155 (0.0109) |
| 2013 | 0.1962 (0.0103) |
| 2014 | 0.2735 (0.0109) |
| 2015 | 0.2745 (0.0324) |
| 2016 | 0.3797 (0.0116) |
| 2019 | 0.4559 (0.0325) |
| 2020 | 0.4209 (0.0388) |
| 2021 | 0.5278 (0.2466) |
| 2022 | 0.3977 (0.0505) |
| 2023 | 0.6403 (0.0507) |
