Researchers who have done studies to examine the relationship between face-to-face contact and birth order have controlled the factors of gender, educational status, age, and geographical distance. These are some of the main factors that account for differences in sibling contact, and researchers needed to eliminate these variables to make their findings more accurate. The quality of sibling relationships and contact is also determined by peer and school/work influences, as well as random events and personal qualities.
In a study done by Thomas Pollet and Daniel Nettle, and with a Netherlands Kinship Panel Study dataset, face to face contact frequency was determined through a survey, asking “How often have you seen *insert sibling* in the past 12 months?” Frequencies ranged from not at all, once a week, to daily. Educational achievement was also recorded in one analysis, while in a second study, geographical distance between siblings was used as an independent variable.BIOLOGICAL FACTORS DETERMINING SIBLING CONTACT
Studies show that in traditional as well as modern societies, more closely related kin provide mutual support more often compared to distantly or unrelated kin. In other words, individuals form closer bonds and have a higher willingness to interact and provide support to fully related siblings than to half siblings or unrelated siblings.
Biological kinship ties can heavily influence interactions, cooperation and mutual investments (both material and social) between individuals. Individuals invest more time and material support in full siblings than half siblings or other distant relatives. In the same way, they are more likely to have conflict with half-siblings or unrelated siblings.
Therefore, in general siblings interact significantly less with each other if they are not fully related.
Since maternal half siblings are more likely to have been raised together than paternal half siblings, a lower percentage of maternal half siblings show a lack of concern for each other than paternal half siblings. This shows that the proximity (cohabitation) of siblings plays an important role in their contact frequency. In a study conducted, more than 35% of Paternal Half Sibling dyads didn’t show any concern for each other, while nearly 25% of Maternal Half Sibling dyads didn’t show concern for each other.
In contrast, the percentage of fully related siblings who don’t spend time with their siblings is dramatically less, only 15%, compared to 25 or 35 percent.
(courtesy of Thomas Pollet, “Evolution and Human Behavior”)SOCIAL FACTORS DETERMINING SIBLING CONTACT
In addition to biological factors, social factors also heavily determine relationships between adult siblings. For example, women are predicted to have stronger relationships with their siblings, hence they are called “kinkeepers”. Also, sister-sister dyads (pairs) are stronger than sister-brother or brother-brother dyads.
Following the individualization theory, higher educated siblings are said to be less concerned with their siblings than lower educated individuals, but financial resources are shown to facilitate sibling contact.
Also, the more similar siblings are, and the closer their age, the stronger their relationship and the more they invest in each other. This is because if siblings have a significant age gap, they are less likely to share the same experiences. Contact frequency of siblings heavily varies with proximity.
Siblings are greatly motivated to maintain contact with each other if they share an emotional bond and a feeling of responsibility towards each other’s welfare. The higher the age, however, the weaker the strength of adult sibling ties. Reasons for sustaining sibling relationships in later life are primarily family events or hardship, commonality, and age-related problems.SIBLING CONTACT WITH PARENTS
Studies have shown that in sibling groups of three or more, the eldest child is usually the most attached to his or her parents. When asked who was the person they were closest to, middleborn children were less likely to give a parent’s name, and more often named a sibling or a close friend. This is supported by the hypothesis that the middle child never receives a period of exclusive attention from the parents, the oldest or youngest sibling. In “sibships” of two, firstborns were more likely to have contact with their parents than lastborns.