| Year | Value (SE) |
|---|---|
| 2008 | 1.3257 (0.2515) |
| 2009 | 0.8213 (0.0773) |
| 2010 | 0.6540 (0.0748) |
| 2011 | 0.9323 (0.0993) |
| 2012 | 0.8657 (0.0821) |
| 2013 | 0.6581 (0.0727) |
| 2014 | 0.6279 (0.0770) |
| 2015 | 0.5061 (0.0882) |
| 2016 | 0.8269 (0.0746) |
| 2017 | 0.8320 (0.0888) |
| 2018 | 0.8880 (0.1154) |
| 2019 | 1.0952 (0.1349) |
| 2020 | 0.8618 (0.2010) |
| 2021 | 0.8170 (0.2663) |
| 2022 | 0.9811 (0.3421) |
| 2023 | 0.7980 (0.1435) |
| 2024 | 0.7883 (0.3820) |
