Relationships among adult full, half, and stepsiblings: Does coresidence explain the stepgap?

Objective
This article aims to compare adult sibling ties of stepsiblings to the ties of full and half-siblings in divorced families, widowed families, and single-parent families.
Background
Siblings are one of the most stable sources of attachment and companionship over the life course and function as important providers of practical and emotional support when going through important life transitions. Due to a steep rise in divorce over the past decades and accompanied increases in remarriage and multipartner fertility, many adults nowadays not only have full siblings, but also half-siblings and stepsiblings.
Method
Using a new module on adult sibling relationships and random- and fixed-effects modeling (OKiN, N = 4506 dyads nested in N = 1742 respondents), we examine the quality of full, half, and stepsibling ties in adulthood and test the main mechanisms driving a potential stepgap in sibling ties: (1) the (absence) of a shared genetic relatedness and (2) the amount of time shared in the same parental household.
Results
The weaker bonds adults, on average, have with their stepsiblings compared to their biological (full and half) siblings are largely explained by the shorter period of time they have lived together during childhood. Nevertheless, a substantial gap remains.
Conclusion
Our results confirm that a stepgap in sibling closeness, contact, and support is visible, but substantially reduced once shared time is considered.