| Year | Value (SE) |
|---|---|
| 2003 | 0.6393 (0.0423) |
| 2007 | 0.5564 (0.1232) |
| 2008 | 0.7432 (0.0594) |
| 2009 | 0.8560 (0.0579) |
| 2010 | 0.8902 (0.0438) |
| 2011 | 0.9088 (0.0548) |
| 2012 | 0.7610 (0.0448) |
| 2013 | 0.6960 (0.0837) |
| 2014 | 0.5852 (0.0740) |
| 2015 | 0.7314 (0.1670) |
| 2018 | 0.7261 (0.0522) |
| 2019 | 0.7138 (0.0853) |
| 2020 | 0.6810 (0.2362) |
| 2021 | 0.6023 (0.2357) |
| 2022 | 0.5807 (0.1166) |
| 2023 | 0.5839 (0.1166) |
