| Year | Value (SE) |
|---|---|
| 2001 | 0.0860 (0.0203) |
| 2002 | 0.3610 (0.0708) |
| 2003 | 0.5960 (0.2559) |
| 2004 | 0.1240 (0.0460) |
| 2005 | 0.2100 (0.1119) |
| 2007 | 0.2720 (0.0752) |
| 2008 | 0.3850 (0.0759) |
| 2009 | 0.2750 (0.0801) |
| 2010 | 0.3720 (0.0890) |
| 2011 | 0.3290 (0.1009) |
| 2012 | 0.1920 (0.0396) |
| 2013 | 0.2950 (0.1033) |
| 2014 | 0.1470 (0.0283) |
| 2015 | 0.2180 (0.2116) |
| 2016 | 0.1510 (0.0453) |
| 2017 | 0.2300 (0.1082) |
| 2018 | 0.3420 (0.0875) |
| 2020 | 0.2780 (0.0617) |
| 2021 | 0.0950 (0.0227) |
| 2022 | 0.2960 (0.0722) |
| 2023 | 0.5140 (0.1112) |
