| Year | |
|---|---|
| 1997 | 266.8 |
| 1998 | 283.7 |
| 1999 | 173.1 |
| 2000 | 192.0 |
| 2001 | 181.1 |
| 2002 | 202.9 |
| 2003 | 211.1 |
| 2004 | 209.6 |
| 2005 | 209.6 |
| 2006 | 211.2 |
| 2007 | 284.0 |
| 2008 | 288.4 |
| 2009 | 287.2 |
| 2010 | 287.1 |
| 2011 | 283.9 |
| 2012 | 288.6 |
| 2013 | 289.3 |
| 2014 | 289.7 |
| 2015 | 285.0 |
| 2016 | 283.5 |
| 2017 | 285.4 |
| 2018 | 281.3 |
| 2019 | 278.4 |
| 2020 | 280.9 |
| 2021 | 274.3 |
| 2022 | 273.8 |
| 2023 | 272.0 |
| 2024 | 284.6 |