| Year | Value (SE) |
|---|---|
| 2002 | 0.7330 (0.1019) |
| 2007 | 1.0370 (0.1152) |
| 2008 | 0.8370 (0.0566) |
| 2009 | 0.7080 (0.0602) |
| 2010 | 0.9280 (0.0495) |
| 2011 | 0.8850 (0.0870) |
| 2012 | 0.9070 (0.0728) |
| 2013 | 0.7320 (0.1176) |
| 2014 | 0.9400 (0.2001) |
| 2015 | 0.7210 (0.1550) |
| 2018 | 0.8960 (0.0664) |
| 2019 | 0.9320 (0.1164) |
| 2020 | 0.8150 (0.1824) |
| 2021 | 0.9410 (0.1878) |
| 2022 | 0.8690 (0.2296) |
| 2023 | 0.6800 (0.1285) |
| 2024 | 0.8050 (0.1357) |
| 2025 | 0.4770 (0.1117) |
