| Frequency | Percentage | Valid percentage | Cumulated Percentage | |
Valid | 2007 | 135 | 23.7 | 23.7 | 23.7 |
2009 | 251 | 44.1 | 44.1 | 67.8 | |
2011 | 183 | 32.2 | 32.2 | 100.0 | |
Total | 569 | 100.0 | 100.0 |
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