| Year | Average price increment |
| 2001 | 81.8 |
| 2002 | 261.89 |
| 2003 | 26.19 |
| 2004 | 314.24 |
| 2005 | 678.11 |
| 2006 | 276.45 |
| 2007 | 1063.12 |
| 2008 | 197.69 |
| 2009 | 382.9 |
| 2010 | 918.58 |
| 2011 | 230.23 |
| 2012 | −64.98 |
| 2013 | 864 |
| 2014 | 965.55 |
| 2015 | 681.75 |