[Morningness-Eveningness for Children Scale: psychometric properties and month of birth effect]

There is strong evidence that individuals can be arranged on a continuum from Eveningness to Morningness reflecting their preferred time range for different activities. This preference, which mostly reflects the phase of the circadian pacemaker, is determined in part by mutations on the CLOCK gene, and by environmental factors such as the month of birth. It has been suggested that eveningness might be a susceptibility factor for depressive disorders. Two self-rated questionnaires are available (the Morningness-Eveningness Questionnaire, MEQ, and the Composite Scale for Morningness) and have been adapted for use with youngsters: the Junior-MEQ and the Morningness-Eveningness Scale for Children (MESC), respectively. Most studies concern adult samples, but it is accepted that puberty is associated with a phase delay in the circadian pacemaker die a shift towards eveningness) occuring around age 12 in both genders. In this study, we examined the psychometric properties of the French version of the MESC in 3 independent samples of adolescents (total n = 392) recruited in the community or during hospitalization in paediatric department, most of them after they attempted suicide. A three-way ANCOVA showed no gender or age effect but rather a strong group effect: hospitalized adolescents scored about 3 points below the community samples (ie towards an eveningness tendency). In each sample, the internal consistency for this 10-item measure was satisfactory (mean alpha = 0.76) and the same two-factor structure was found (Morningness and Planification) as shown by procrustes rotations. As expected, there was a negative correlation between the MESC scores and reported times of rising, of going to bed, of best intellectual and physical performances, but no correlation with the number of minutes of sleep needed. The test-retest stability was acceptable within a 8-month delay although the sample size was limited (n = 20). In line with literature data, we found a modest negative correlation about -0.20 in 2 of the samples with two depression measures (MADRS and CES-D). Finally, we assessed the effect of the month of birth on the MESC total score by a non-linear regression adjusted for age and gender that included a one-cycle cosinus function. We found that birth in March-April was associated with eveningness while birth in September-October was associated with morningness. The peak and nadir occur two months before those found in a large sample of young adults. However, this result could not be replicated in the sample of hospitalized adolescents suggesting that the effect might have been smoothed by a "pathological" factor. Reasons for this descrepancy and implications for developmental psychiatry are discussed. More precisely, we postulate a relationship between morningness and impulsivity-related personality traits. In conclusion, the MESC is a psychometrically sound instrument in need of further validity assessment.