| Year | Value (SE) |
|---|---|
| 2008 | 1.0258 (0.2007) |
| 2009 | 0.9678 (0.0570) |
| 2010 | 0.9699 (0.1046) |
| 2011 | 0.9324 (0.0498) |
| 2012 | 0.8958 (0.0400) |
| 2013 | 0.9824 (0.1249) |
| 2014 | 1.0311 (0.1243) |
| 2015 | 1.0293 (0.2560) |
| 2016 | 0.8993 (0.0370) |
| 2017 | 0.9492 (0.0591) |
| 2019 | 1.0511 (0.1108) |
| 2020 | 1.2690 (0.3196) |
| 2021 | 2.7462 (2.7093) |
