Estimating Reliability of Within-Person Couplings in a Multilevel Framework

Area of Science:

• Psychology
• Behavioral Science
• Psychometrics

Background:

• Within-person couplings are key in psychological research, predicting behavior and health outcomes.
• Stress reactivity, a specific coupling, is often treated as a stable personality trait.
• The reliability of these within-person couplings has been largely neglected.

Purpose of the Study:

• To introduce a novel reliability index for within-person couplings.
• To assess the reliability and test-retest stability of stress reactivity estimates.
• To guide researchers in maximizing reliability in future studies.

Main Methods:

• Development of a user-modifiable R code for reliability estimation.
• Simulation study to evaluate the index's performance with unbalanced data.
• Application of the index in a measurement burst study using a daily diary design.

Main Results:

• The proposed reliability index performs well, even with missing data.
• Reliability and test-retest correlations for stress reactivity estimates were found to be low.
• This challenges the assumption of stress reactivity as a stable, person-level variable.

Conclusions:

• The reliability of within-person couplings, particularly stress reactivity, is lower than often assumed.
• Researchers should carefully consider factors influencing reliability when studying interindividual differences in couplings.
• The developed index and methodology can enhance the rigor of psychological research on within-person variability.