| Year | Value (SE) |
|---|---|
| 2008 | 0.7757 (0.0340) |
| 2009 | 0.7023 (0.0229) |
| 2013 | 0.4748 (0.0289) |
| 2014 | 0.5701 (0.0277) |
| 2015 | 0.6621 (0.1158) |
| 2016 | 0.6681 (0.0520) |
| 2017 | 0.7089 (0.0315) |
| 2018 | 0.6786 (0.0317) |
| 2019 | 0.4694 (0.0361) |
| 2020 | 0.5344 (0.1242) |
| 2021 | 0.5630 (0.1700) |
| 2022 | 0.6397 (0.1701) |
| 2023 | 0.7038 (0.0550) |
