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 seven days, implying variability in temperament traits’ expressions. In two daily diary studies, we used the whole trait theory perspective to investigate whether infant temperament is observable daily and to what degree it 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 and total observations: 984). The results suggest a substantial within-person variation in daily infant temperament (ICCs: .41–.54). Study 2 ( N = 199 mothers, median number of days: 7, and total observations: 1375) replicated these results on the variability in infant state temperament (ICCs: .41–.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.