| Year | Average | 10th percentile | 90th percentile | Target value |
|---|---|---|---|---|
| 2006 | 18.7 | 11.3 | 31.5 | 25 |
| 2007 | 17.2 | 10.3 | 26.4 | 25 |
| 2008 | 17.6 | 9.7 | 26.8 | 25 |
| 2009 | 17.4 | 11.1 | 25.0 | 25 |
| 2010 | 18.5 | 10.4 | 27.9 | 25 |
| 2011 | 19.1 | 11.4 | 29.9 | 25 |
| 2012 | 17.2 | 10.3 | 27.7 | 25 |
| 2013 | 16.4 | 9.5 | 26.0 | 25 |
| 2014 | 15.6 | 9.6 | 24.3 | 25 |