Table 1.

Descriptive statistics ofparticipants of the longitudinal study in Trier, Germany.

Grade	Sex	2008/2009		2009/2010		2010/2011		2011/2012
		N	Age	N	Age	N	Age	N	Age
1	Boys	310	6.86 ± 0.44	358	6.80 ± 0.42
1	Girls	313	6.80 ± 0.45	381	6.76 ± 0.43
2	Boys			321	7.84 ± 0.66	337	7.93 ± 0.46
2	Girls			344	7.81 ± 0.47	360	7.91 ± 0.46
3	Boys					309	8.95 ± 0.52	234	9.20 ± 0.46
3	Girls					312	8.98 ± 0.50	239	9.09 ± 0.75
4	Boys							204	10.16 ± 0.51
4	Girls							222	10.17 ± 0.52
Total		623	6.83 ± 0.45	1404	7.27 ± 0.72	1318	8.41 ± 0.71	899	9.63 ± 0.77