Stewart, Robert B.
Stewart, R.B., Mobley, L.A., Van Tuyl, S.S., & Salvador, M.A. (1987). The firstborn's adjustment to the birth of a sibling: A longitudinal assessment. Child Development, 58, 341-355.
Stewart, R.B. (1983). Sibling attachment relationships: Child-infant interactions in the Strange Situation. Developmental Psychology, 19, 192-199.