| Year | Value (SE) |
|---|---|
| 2008 | 0.3657 (0.0367) |
| 2009 | 0.4923 (0.0209) |
| 2010 | 0.3567 (0.0955) |
| 2011 | 0.4438 (0.0109) |
| 2012 | 0.4939 (0.0119) |
| 2013 | 0.5955 (0.0437) |
| 2014 | 0.6984 (0.0271) |
| 2015 | 0.5458 (0.0913) |
| 2016 | 0.6466 (0.0331) |
| 2017 | 0.6240 (0.0372) |
| 2018 | 0.6478 (0.0675) |
| 2019 | 0.2166 (0.0237) |
| 2020 | 0.7897 (0.2553) |
| 2021 | 0.4995 (0.5853) |
| 2022 | 0.4970 (0.1086) |
