| Year | Value (SE) |
|---|---|
| 2002 | 0.9200 (0.0253) |
| 2003 | 0.8660 (0.0177) |
| 2004 | 0.9260 (0.0080) |
| 2006 | 0.9450 (0.0088) |
| 2008 | 0.9400 (0.0187) |
| 2009 | 0.9270 (0.0105) |
| 2010 | 1.0330 (0.0436) |
| 2011 | 0.9300 (0.0156) |
| 2013 | 0.8970 (0.0289) |
| 2014 | 0.9210 (0.0240) |
| 2016 | 0.9550 (0.0198) |
| 2019 | 0.9270 (0.0199) |
