Zajonc R B, Markus H, Markus G B
J Pers Soc Psychol. 1979 Aug;37(8):1325-41. doi: 10.1037//0022-3514.37.8.1325.
Studies relating intellectual performance to birth order report conflicting results, some finding intellectual scores to increase, others to decrease with birth order. In contrast, the relationship between intellectual performance and family size is stable and consistently replicable. Why do these two highly related variables generate such divergent results? This birth order puzzle is resolved by means of the confluence model that quantifies the influences upon intellectual growth arising within the family context. At the time of a new birth, two opposing influences act upon intellectual growth of the elder sibling: (a) his or her intellectual environment is "diluted" and (b) he or she loses the "last-born's handicap" and begins serving as an intellectual resource to the younger sibling. Since these opposite effects are not equal in magnitude, the differences in intellectual performance among birth ranks are shown to be age dependent. While elder children may surpass their younger siblings in intellectual performance at some ages, they may be overtaken by them at others. Thus when age is taken into consideration, the birth order literature loses its chaotic character and an orderly pattern of results emerges.
将智力表现与出生顺序相关的研究报告了相互矛盾的结果，一些研究发现智力分数会随着出生顺序的增加而提高，另一些则发现会降低。相比之下，智力表现与家庭规模之间的关系是稳定且可重复验证的。为什么这两个高度相关的变量会产生如此不同的结果呢？这个出生顺序谜题通过融合模型得以解决，该模型量化了家庭环境中对智力成长产生的影响。在新生儿出生时，两种相反的影响作用于年长同胞的智力成长：（a）其智力环境被“稀释”；（b）他或她失去了“最小孩子的劣势”，并开始成为年幼同胞的智力资源。由于这些相反的影响在程度上并不相等，出生顺序不同导致的智力表现差异被证明与年龄有关。虽然年长的孩子在某些年龄段的智力表现可能超过年幼的同胞，但在其他年龄段可能会被他们超越。因此，当考虑到年龄因素时，关于出生顺序的文献不再呈现混乱的特征，而是出现了有序的结果模式。
