Measuring Developmental Differences With an Age-of-Attainment Method

The sensitive measurement of variation in rate of attainment is anunderutilized but useful indicator of individual differences in development. To assesssuch individuality, we used longitudinal parental diary checklists of infant attainmentsto estimate the ages at which ubiquitous developmental milestones like sitting andwalking were reached. Parents using this diary checklist have been shown to be validreporters of milestone attainments. Present analyses show that multiple definitions ofmilestone onset have high reliability as well. Babies differ considerably in their ratesof development, and such individual differences in rates may be predicted from othervariables with survival (event history) analysis. Ages of attainment for sustainedsitting, crawling, and walking were calculated for 519 infants and predicted using 11common covariates. Our discovery that babies of younger mothers reach these milestonessooner than those of older mothers reveals the value of an age-of-attainment (AOA)approach. A framework with a SAS program for collecting and analyzing AOA data ispresented