To assess the impact of varying definitions of excessive crying and infantile colic on prevalence estimates and to assess to what extent these definitions comprise the same children.
Parents of 3345 infants aged 1, 3, and 6 months (response: 96.5%) were interviewed on the crying behavior of their infant in a Dutch cross-sectional national population-based study. We computed the prevalence of excessive crying according to 10 published definitions regarding parent-reported duration of infant crying and the parents' experience. We measured concordance between pairs of definitions by Cohen's κ (agreement adjusted for chance agreement).
Overall prevalence rates of excessive crying varied strongly between definitions, from 1.5% to 11.9%. They were always highest in 1-month-old infants. Concordance between definitions was only excellent (κ > 0.75) if they were closely related, such as crying for >3 hours/day for >3 days/week for the preceding 2 or 3 weeks. Concordance between less closely related definitions was much weaker. Concordance between definitions that were based on duration and on parental experience was mostly poor (κ: 0.17–0.53 for infants aged 1 and 3 months).
Different definitions of excessive crying lead to the inclusion of very dissimilar groups of infants. We recommend presenting study results using clearly described definitions, preferably concerning both duration of crying and parental distress. This may improve the comparability of studies on the cause and treatment of excessive infant crying. The impact of the method of data collection on this comparability needs additional study.colic, preventive child health care, prevention, infancy.