a decreasing trendp < 0.001
However, it showed a decreasing trend by grade among boys (9th grade: 8.09 ± 1.5; 10th grade :7.98 ± 1.52; 11th grade: 7.88 ± 1.57; 12th grade 12: 7.64 ± 1.73; p < 0.001) and girls alike (9th grade: 8.12 ± 1.45; 10th grade: 7.91 ± 1.50; 11th grade: 7.86 ± 1.53; grade 12: 7.85 ± 1.55; p = 0.018).