| Characteristic | Years | ||||||
| 2005 | 2006 | 2007 | 2008 | 2009 | 2011 | 2012 | |
| School background |
|
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|
|
|
|
|
| Private school | 55.7 | 55.5 | 57.3 | 58.2 | 56.4 | 57.3 | 55.2 |
| Public school | 44.3 | 44.5 | 42.7 | 41.8 | 43.6 | 42.7 | 44.8 |
| Total | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 | 100.0 |