| Year | Value (SE) |
|---|---|
| 2006 | 0.3230 (0.0407) |
| 2007 | 0.6490 (0.0487) |
| 2008 | 0.3350 (0.0526) |
| 2009 | 0.2120 (0.0286) |
| 2010 | 0.4700 (0.0475) |
| 2011 | 0.1790 (0.0247) |
| 2012 | 0.4500 (0.0297) |
| 2013 | 0.4620 (0.0481) |
| 2014 | 0.4220 (0.0564) |
| 2015 | 0.2910 (0.0586) |
| 2016 | 0.3910 (0.0420) |
| 2017 | 0.3700 (0.0333) |
| 2018 | 0.4110 (0.0452) |
| 2019 | 0.3850 (0.1275) |
| 2020 | 0.3310 (0.0418) |
| 2021 | 0.6280 (0.1180) |
| 2022 | 0.7700 (0.2460) |
| 2023 | 0.4010 (0.0502) |
| 2024 | 0.2380 (0.0636) |
