Threshold regression corroborates the inverted U: performance gains below 7–9 h and significantly negative coefficients beyond the second threshold¶

Claim · All claims
Evidence · 1 study · associational r2 · q2
Currency · newest study 2025 · not yet checked against its sources · not reviewed by a person

Subclaims¶

q2 i? Beyond the second detected threshold (8–9 h for Chinese, math, science), regression coefficients on sleep became significantly negative. → Wang 2025

Evidence¶

Wang 2025¶

Wang, M., Chen, Z., Han, N., & Yao, H. (2025). Sleep duration and subject-specific academic performance among adolescents in China. npj Science of Learning. https://doi.org/10.1038/s41539-025-00361-y

q2 · i? · associational · r2

Double-threshold regression for Chinese, mathematics, and science detected two significant thresholds between 7–8 h and 8–9 h; coefficients rose markedly in the 7–9 h window before turning negative above it.

"once sleep exceeded the second threshold (8-9 h), the coefficients became significantly negative, implying that excessive sleep duration may be associated with lower academic outcomes."

Discussion¶

Learner Variables¶

• Sleep — predictor: learners who differ on it differ in outcomes

Related Claims¶

• Sleep duration shows an inverted U-shaped association with academic performance in all five subjects, with a peak around 8 hours of nightly sleep — related
• Optimal sleep duration varies by subject: about 8–9 hours for mathematics and 7–8 hours for Chinese, English, science, and arts — related
• Sleep duration contributes more to variance in Chinese, mathematics, and science performance than to English and arts, but less than socioeconomic status in every subject — related