| Year | Value (SE) |
|---|---|
| 2007 | 0.5810 (0.0150) |
| 2008 | 0.3360 (0.0117) |
| 2009 | 0.3670 (0.0074) |
| 2010 | 0.4270 (0.0176) |
| 2011 | 0.5210 (0.0072) |
| 2012 | 0.4730 (0.0077) |
| 2013 | 0.5670 (0.0113) |
| 2014 | 0.6470 (0.0081) |
| 2015 | 0.6980 (0.0359) |
| 2016 | 0.6760 (0.0065) |
| 2017 | 0.6050 (0.0106) |
| 2018 | 0.5200 (0.0127) |
| 2019 | 0.4820 (0.0186) |
| 2020 | 0.6940 (0.0210) |
| 2021 | 0.6430 (0.0171) |
| 2022 | 0.7110 (0.0179) |
| 2023 | 0.5810 (0.0088) |
| 2024 | 0.5580 (0.0253) |
