| Year | Average | 10th percentile | 90th percentile | Limit value |
|---|---|---|---|---|
| 2006 | 18.4 | 11.2 | 31.4 | 25 |
| 2007 | 16.6 | 9.9 | 25.6 | 25 |
| 2008 | 17.6 | 9.7 | 25.1 | 25 |
| 2009 | 17.3 | 11.6 | 24.4 | 25 |
| 2010 | 18.1 | 10.4 | 27.9 | 25 |
| 2011 | 18.7 | 11.4 | 29.2 | 25 |
| 2012 | 16.9 | 10.8 | 26.8 | 25 |
| 2013 | 15.8 | 9.5 | 23.4 | 25 |
| 2014 | 15.1 | 9.6 | 23.7 | 25 |
| 2015 | 14.8 | 9.1 | 23.6 | 25 |