| Year | Rate |
|---|---|
| 2024 | $30,900 |
| 2023 | $29,100 |
| 2022 | $27,700 |
| 2021 | $27,300 |
| 2020 | $26,400 |
| 2019 | $25,400 |
| 2018 | $24,700 |
| 2017 | $25,400 |
| 2016 | $25,500 |
| 2015 | $24,700 |
| 2014 | $24,500 |
| 2013 | $23,800 |
| 2012 | $23,000 |
| 2011 | $22,300 |
| 2010 | $22,800 |
| 2009 | $21,500 |
| 2008 | $20,100 |
| 2007 | $18,100 |
| 2006 | $17,100 |
| 2005 | $16,400 |
| 2004 | $15,900 |
| 2003 | $14,700 |
| 2002 | $14,700 |