They found that the negative effect of sibship size (the amount of siblings in an immediate family) on educational attainment was cut in half between the beginning and middle of the 20th century. (sciencedaily.com)
They studied groups of siblings, called sibships, in which one member was at least 98 and had at least one brother older than 91 or sister older than 95. (scientificamerican.com)
The data for the present paper were collected from the 311 families at T2 in which there were three or more living offspring; this is the minimum sibship size necessary for siblings to differentiate among group members. (academic.oup.com)