We examine the effects of biological relatedness vis-à-vis shared residence on the strength of adult intergerenational ties using a new multi-actor survey where respondents raised in complex families were systematically oversampled. A unique feature of the survey is that it allows for a double multiactor design. We sampled children 25-45 years old, called ‘anchors’ (N = 6,485). All parent figures of these children – called ‘alters’ – were found via the registers and also participated in the study (N = 9,325). The anchor data make it possible to apply a multiple parent design where the children are the higher-level units (level 2) and the parents are the lower-level units (level 1). We asked the alters about the relationship they have to all their adult children, yielding a multiple child design, where parents are the level-2 units of analysis and adult children are he level-1 units. Using fixed-effects models, we then make direct comparisons within the level-2 units. In the multiple parent design, this implies making comparisons among different types of parents within adult children. For example, we compare how much contact a daughter has with her divorced father to how much contact she has with her stepfather. Implicitly, this approach controls for the influence of all unobservable child characteristics. In the multiple child design, the fixed-effects model implies that we compare different types of children within each parent. For example, we compare the closeness a father feels to his current biological children to the closeness he feels to his stepchildren. This approach controls for all unobservable parent characteristics. By combining the two within-family designs in one study, the goal is to get closer to the causal nature of the effects of biology vis-à-vis shared residence.