| Year | Value (SE) |
|---|---|
| 2002 | 0.9030 (0.0359) |
| 2003 | 0.9720 (0.0316) |
| 2004 | 0.8630 (0.0128) |
| 2006 | 0.9770 (0.0123) |
| 2008 | 0.9600 (0.0297) |
| 2009 | 1.0130 (0.0231) |
| 2010 | 0.8230 (0.0500) |
| 2011 | 0.9950 (0.0284) |
| 2013 | 1.0350 (0.0563) |
| 2014 | 0.9540 (0.0460) |
| 2016 | 1.0080 (0.0445) |
| 2019 | 0.9870 (0.0384) |
