The stability of joint engagement states in infant siblings of children with and without ASD: Implications for measurement practices.

Obtaining stable estimates of caregiver-child joint engagement states is of interest for researchers who study development and early intervention in young children with autism spectrum disorder (ASD). However, studies to date have offered little guidance on the numbers of sessions and coders necessary to obtain sufficiently stable estimates of these constructs. We used procedures derived from G theory to carry out a generalizability study, in which we partitioned error variance between two facets of our system for measuring joint engagement states: session and coder. A decision study was then conducted to determine the number of sessions and coders required to obtain g coefficients of 0.80, an a priori threshold set for acceptable stability. This process was conducted separately for 10 infant siblings of children with ASD (Sibs-ASD) and 10 infants whose older sibling did not have ASD (Sibs-TD), and for two different joint engagement states; lower- and higher-order supported joint engagement (LSJE and HSJE, respectively). Results indicated that, in the Sibs-ASD group, four sessions and one coder was required to obtain acceptably stable estimates for HSJE; only one session and one coder were required for LSJE. In the Sibs-TD group, two sessions and one coder were required for HSJE; seven sessions and two coders were required for LSJE. Implications for measurement in future research are discussed. Autism Res 2019, 12: 495-504