| Year | Value (SE) |
|---|---|
| 2008 | 1.0572 (0.2911) |
| 2009 | 0.7989 (0.1386) |
| 2010 | 0.8807 (0.2151) |
| 2011 | 1.1218 (0.1582) |
| 2012 | 0.9499 (0.1354) |
| 2013 | 1.1602 (0.2526) |
| 2014 | 0.8346 (0.1776) |
| 2015 | 0.7511 (0.1875) |
| 2016 | 0.5187 (0.0840) |
| 2018 | 0.6842 (0.2084) |
| 2019 | 0.9495 (0.2258) |
| 2020 | 1.4609 (0.9320) |
| 2022 | 0.6594 (0.3558) |
| 2023 | 0.8369 (0.3160) |
