| Year | Value (SE) |
|---|---|
| 2008 | 0.5240 (0.0768) |
| 2009 | 0.5840 (0.0573) |
| 2010 | 0.6150 (0.0502) |
| 2011 | 0.6310 (0.0461) |
| 2012 | 0.5330 (0.0326) |
| 2013 | 0.4150 (0.0388) |
| 2014 | 0.4320 (0.0306) |
| 2015 | 0.3590 (0.0520) |
| 2016 | 0.5030 (0.0275) |
| 2017 | 0.5020 (0.0330) |
| 2018 | 0.4200 (0.0354) |
| 2019 | 0.4590 (0.0574) |
| 2020 | 0.4750 (0.0786) |
| 2021 | 0.5350 (0.0911) |
| 2022 | 1.2450 (0.5423) |
| 2023 | 0.2790 (0.0376) |
