Morningness-Eveningness Questionnaire: Reliability and factorial structure of the full and reduced versions in Spanish adolescents.

This study analyzed the suitability of the Morningness-Eveningness Questionnaire (MEQ) for Spanish adolescents, focusing on reliability, structure, and age/sex invariance. 2,268 adolescents (49.1% girls, aged 12-17) participated. Four MEQ items were unsuitable, leading to a 15-item version (MEQ-15) with good reliability and fit to a bifactor model: general morningness-eveningness factor and awakening time, sleep time, and time of greatest efficiency factors. The reduced MEQ (rMEQ) also fit a one-factor model. Sex and age invariance were tenable for the general factor of MEQ-15 and rMEQ. Morningness declines during adolescence, with boys showing more morningness than girls. Both versions show good psychometric properties.