Morningness-eveningness and lifestyle regularity

The relation between morningness (M) - eveningness (E) and lifestyle regularity was studied in a convenience sample of 100 healthy subjects aged between 20 and 59 yrs (47 males and 53 females; mean age 33.6 yrs). Morningness-eveningness was measured by a single administration of the 13-item Composite Scale for Morningness (CSM). Lifestyle regularity was measured by requiring subjects to complete a five-item Social Rhythm Metric diary (SRM-5) each evening for two weeks. Each week of SRM-5 was analyzed separately and the two SRM scores averaged to yield the lifestyle regularity measure for the subject. Subjects were categorized by morningness into top and bottom quartiles of CSM score (denoted M-types and E-types, respectively), with the remaining 50% of subjects denoted as intermediate (I-types). Mean SRM scores significantly differed between the three morningness groups (p < 0.001) in the order E-types (SRM = 3.6), then I-types (SRM = 4.0), then M-types (SRM = 4.9), with higher scores indicating greater daily lifestyle regularity. The effect size of the E-type versus M-type difference was approximately 1.3. The relationship between the CSM and SRM scores was also confirmed using a correlational analysis (rho = 0.428; p < 0.001). This correlational finding was substantially weaker when age was partialed out (r = 0.186; p = 0.065), although there was still a trend toward a significant relationship. Thus it appears that morning types appear to be more regular in their daily lifestyle than are evening types, suggesting a relationship between these two aspects of human circadian behavior.