| Year | N | N mean | N z-score | N (%) |
| 2006 | 0.70786 | 0.6388 | 0.92508 | 83 |
| 2007 | 0.93935 | 0.77681 | 9.9461 | 100 |
| 2008 | 0.97504 | 0.85018 | 32.3538 | 100 |
| 2009 | 0.97416 | 0.87122 | 46.7369 | 100 |
| 2010 | 0.98042 | 0.88464 | 53.5509 | 100 |
| 2011 | 0.97216 | 0.88152 | 51.4986 | 100 |
| 2012 | 0.96885 | 0.88319 | 53.457 | 100 |
| 2013 | 0.97329 | 0.89418 | 44.7661 | 100 |