| Year | Value (SE) |
|---|---|
| 2008 | 0.8193 (0.1498) |
| 2009 | 0.8387 (0.0955) |
| 2010 | 0.8409 (0.1360) |
| 2011 | 0.9212 (0.0739) |
| 2012 | 0.8589 (0.0654) |
| 2013 | 0.7412 (0.0935) |
| 2014 | 0.7013 (0.0628) |
| 2015 | 0.5304 (0.1274) |
| 2016 | 0.6667 (0.0498) |
| 2017 | 0.7869 (0.0849) |
| 2018 | 0.7289 (0.0862) |
| 2019 | 1.1316 (0.1792) |
| 2020 | 1.0426 (0.4328) |
| 2021 | 1.4283 (1.0738) |
| 2022 | 3.4251 (1.9362) |
| 2023 | 0.4689 (0.1266) |
