| Year | |
|---|---|
| 1997 | 79.7 |
| 1998 | 75.7 |
| 1999 | 59.6 |
| 2000 | 59.1 |
| 2001 | 53.5 |
| 2002 | 58.6 |
| 2003 | 61.1 |
| 2004 | 65.9 |
| 2005 | 72.8 |
| 2006 | 71.9 |
| 2007 | 78.9 |
| 2008 | 80.7 |
| 2009 | 69.7 |
| 2010 | 73.9 |
| 2011 | 68.8 |
| 2012 | 66.3 |
| 2013 | 67.9 |
| 2014 | 67.4 |
| 2015 | 66.5 |
| 2016 | 70.0 |
| 2017 | 73.4 |
| 2018 | 74.6 |
| 2019 | 71.2 |
| 2020 | 70.7 |
| 2021 | 70.6 |
| 2022 | 72.3 |
| 2023 | 69.0 |
| 2024 | 65.9 |