Table 3.

Chi square test for comparing equal proportions of myopia for the different risk factors

Grouping characteristic	Chi^2 test statistic	Degrees of freedom	P-value
School	51.237	3	< 0.0001
Age group (above and below 10)	7.689	1	0.0056
Gender	9.597	1	0.0019
Sport (every day versus not every day)	11.847	1	0.0006 (43 missing observations)
Time in front of the screen (less than 4 h versus more or equal to 4 h)	1.4638	1	0.2263 (59 missing observations)
Previous examinations	48.134	1	< 0.0001 (12 missing observations)
Parents wear glasses (at least one of the parents to wear glasses versus none of them)	20.928	1	< 0.0001 (76 missing observations)