| Year | Value (SE) |
|---|---|
| 2006 | 0.6174 (0.1023) |
| 2007 | 0.8746 (0.1653) |
| 2008 | 0.5111 (0.1153) |
| 2009 | 0.5887 (0.1006) |
| 2010 | 0.6737 (0.1315) |
| 2011 | 0.5597 (0.0955) |
| 2012 | 0.6873 (0.0601) |
| 2013 | 0.7923 (0.1178) |
| 2014 | 0.9386 (0.1625) |
| 2015 | 0.6709 (0.2088) |
| 2016 | 0.6507 (0.0883) |
| 2017 | 0.7278 (0.1079) |
| 2018 | 0.6425 (0.1061) |
| 2019 | 1.4520 (0.6113) |
| 2020 | 0.5305 (0.2013) |
| 2021 | 0.7646 (0.6081) |
| 2022 | 0.8649 (0.4633) |
| 2023 | 0.4917 (0.1154) |
| 2024 | 0.4230 (0.2441) |
