The comparability with the international literature is a decisive criterion for the choice of test instruments. Therefore, German translations of the Morningness-Eveningness Questionnaire (MEQ, Horne & Östberg, Int J Chronobiol 4:97–110, 1976) are used to identify the subjective circadian phase (chronotype). In the present study the validity of a German version of the MEQ (D-MEQ) has been ... [Show full abstract] examined. Criteria were the validated questionnaire for the subjective circadian phase (SCP, R Moog, in Reinberg, Vieux, Andlauer (eds): night and shift work. Biological and social aspects. Pergamon Press Oxford, 1981) as well as the nadir of core body temperature and the onset of nocturnally elevated salivary melatonin concentration.
377 persons (207 women, 170 men, 18–68 years) completed both questionnaires (ever half of them first either the D-MEQ or the SCP). Forty-three persons completed the D-MEQ again 7 to 12 weeks later. Fifty persons were observed during a 24 hours constant routine, where they kept a strict bedrest at low illumination levels (<30 lux), an ambient temperature of 20°C and an hourly isocaloric diet. Rectal temperature was continuously registered throughout and salivary melatonin concentration was determined hourly.
The scores of both questionnaires correlated significantly (r=−0.9, p<0.0001) and resulted in an almost equal number of assignments to the various diurnal types. The latter correlated in turn significantly with the nadir of body core temperature (r=−0.345, p<0.014) and with the onset of nocturnally elevated melatonin synthesis (r=−0.606, p<0.0001).
Hence, the German version of the MEQ applied here is a valid instrument for the identification of the individual circadian phase.