| Year | Value (SE) |
|---|---|
| 2008 | 0.8193 (0.0914) |
| 2009 | 0.9316 (0.0548) |
| 2010 | 0.7775 (0.1138) |
| 2011 | 0.8453 (0.0297) |
| 2012 | 0.8324 (0.0395) |
| 2013 | 0.7943 (0.0712) |
| 2014 | 0.7948 (0.0450) |
| 2015 | 0.9939 (0.1904) |
| 2016 | 0.8678 (0.0448) |
| 2017 | 0.8146 (0.0718) |
| 2018 | 0.9276 (0.0802) |
| 2019 | 0.7793 (0.0776) |
| 2020 | 0.9659 (0.3679) |
| 2021 | 0.7518 (0.5506) |
| 2022 | 0.7880 (0.2839) |
| 2023 | 0.6072 (0.1426) |
