Chronotype description: In search of a solid subjective amplitude scale

Area of Science:

• Chronobiology
• Psychometrics
• Sleep Research

Background:

• Subjective circadian amplitude (AM) reflects diurnal arousal variations, but its measurement is challenging due to construct complexity.
• Existing chronotype questionnaires have unsatisfactory psychometric properties for assessing AM distinctness.
• A robust scale is needed to accurately quantify subjective circadian amplitude.

Purpose of the Study:

• To develop and validate a new scale for measuring subjective circadian amplitude (AM).
• To assess the psychometric properties of the newly developed AM scale.
• To explore the relationship between AM and morning-eveningness (ME) chronotype.

Main Methods:

• Rasch analysis was applied to 12 behavioral descriptors of circadian rhythm distinctness.
• A four-point scale was developed based on Rasch analysis, comprising eight items (four for small AM, four for large AM).
• Data from 234 subjects were analyzed using Principal Component Analysis (PCA) and correlation analyses.

Main Results:

• The Rasch analysis confirmed the unidimensionality of the subjective amplitude construct.
• The newly developed four-point AM scale demonstrated satisfactory fit statistics and internal reliability (Cronbach's alpha = 0.72).
• No significant correlation was found between the AM and ME scales (r = -0.018).

Conclusions:

• The newly developed subjective amplitude scale is a psychometrically sound instrument for measuring diurnal arousal variations.
• Subjective amplitude appears to be a distinct dimension from morning-eveningness, potentially reflecting the circadian component of sleep regulation.
• Distinct diurnal arousal changes may be linked to emotional lability and susceptibility to mood disorders.