How was your child’s temperament today and last week? Considering within-person variability in the measurement of infant temperament

Abstract

Infant temperament is usually considered biologically driven and a precursor of personality. Despite being conceived as trait measures, parent reports for assessing infant temperament use short timescales, for example, the past 7 days, implying variability in temperament traits' expressions. In two daily diary studies, we use the perspective of whole-trait theory to investigate whether infant temperament is observable on a daily basis and to what degree infant temperament varies within-person across days. In Study 1, N = 137 mothers of infants aged 6-18 months reported on their infant’s daily (state) temperament (median number of days: 8, total observations: 984). The results suggest a substantial within-person variation in daily infant temperament (ICCs: .41 to .54). Study 2 (N = 199 mothers, median number of days: 7, total observations: 1375) replicated these results on the variability in infant state temperament (ICCs: .41 to .51). In addition, infant state temperament was related to infant trait temperament. However, certain temperament items – primarily those assessing surgency – were frequently rated as not applicable and did not seem suitable for daily assessments. Across both studies, results indicate substantial within-person variability in daily infant temperament and a strong trait component.