| Year | Value (SE) |
|---|---|
| 2003 | 0.8900 (0.0201) |
| 2007 | 0.8230 (0.0852) |
| 2008 | 0.8640 (0.0234) |
| 2009 | 1.0410 (0.0304) |
| 2010 | 0.8780 (0.0507) |
| 2011 | 0.9370 (0.0140) |
| 2012 | 0.9150 (0.0222) |
| 2013 | 1.0010 (0.0683) |
| 2014 | 0.9150 (0.0469) |
| 2015 | 0.9430 (0.0793) |
| 2018 | 0.9420 (0.0351) |
| 2019 | 0.9220 (0.0448) |
| 2020 | 0.8500 (0.1197) |
| 2021 | 1.3140 (0.3304) |
| 2022 | 0.8770 (0.0522) |
| 2023 | 0.9390 (0.0579) |
