Beyond larks and owls: Revisiting the circadian typology using the MESSi scale and a cluster-based approach.

Chronopsychological research typically applied the morningness-eveningness dimension, resulting in a distinction between morning, intermediate, and evening chronotypes. However, in recent years, new measures have been developed that transcend the traditional "morning larks" vs. "night owls" dichotomy and better capture the complexity of individual differences in circadian rhythmicity. One such measure that addresses the multidimensional character of the circadian rhythm is the Morningness-Eveningness-Stability Scale improved (MESSi) which comprises three dimensions: morning affect, eveningness, and distinctness. However, delineating specific chronotypes using the cut-off points, as was commonly done for other established scales, is not possible in the case of MESSi due to its multidimensionality. In the present paper, we provide a first attempt to introduce a cluster-based approach to deal with MESSi scores. For this purpose, we determined the number of clusters to be extracted using data from our previous study conducted in Poland (N = 1106). Next, we attempted to replicate this cluster solution in another Polish sample (N = 768) and a German sample (N = 637). Finally, we also intended to illustrate how individuals assigned to the established clusters differ in terms of sleep parameters and other differential variables such as positive and negative affect, personality traits, depressive and anxiety symptoms, self-regulation, and self-efficacy. After segmenting MESSi scores by cluster analysis in the three samples we found support for a four-cluster solution, including four circadian profiles which we propose to label "intermediate-finches", "hardy larks", "night owls", and "vulnerable larks". This is the first attempt to introduce a cluster-based, multi-dimensional approach to dealing with MESSi scores.