本論文主要在探討異質群體網路的建構問題。我們假設群體內及群體外的連結成本相同，但是不同群體內較常發生的問題不同，每個人均可能發生自己所屬群體內（較常發生）的問題以及非所屬群體（較不常發生）的問題。在這樣的假設下我們分別探討線性成本、邊際成本遞增下的對稱均衡及非對稱均衡。線性成本下，每個人會偏好擁有較多群體內連結數、較少群體外連結數，而連結強度不是1就是0，但是1或0是經濟個體的內生選擇，和Jackson and Rogers(2005)、Galeotti et al.(2006)假設強度不是1就是0的情況不同。當邊際成本為遞增，多數時候人們會偏好較多、較強的群體內連結;較少、較弱的群體外連結，所以遞增成本模型可以解釋現實社會人們傾向和同群體的人保持較多、較強關係的現像。 若每個人的潛在可連結數一樣，則無論在線性成本或邊際成本遞增之下，對稱均衡都是最有效率的均衡型態;而若每個人潛在可連結數不一樣，經濟個體較有意願跟潛在可連結數較小的人維持較緊密的關係。另外，和線性成本比較，若邊際成本是遞增型態，就某個群體內的連結狀況來說，經濟個體會偏好較多連結數、較弱強度的模式，因此群體內的群聚現像明顯，符合實證研究的結果。

Many empirical and theoretical studies show that workers obtain jobs through their social contacts. This paper attempts to investigate how the difference of individuals’ intrinsic abilities in obtaining their jobs affects the social network structure that emerges. When the probability of players who get job information by themselves is large enough, low-ability players will maintain more contacts than high-ability players do. We analyze the equilibrium network structures in homogeneous society and heterogeneous society respectively. For analyzing more complex cases that people are heterogeneous in their ability of obtaining jobs, we suggest a new equilibrium concept: Forward Induction Network Equilibrium (FINE), a refinement of pairwise stability equilibrium. According to FINE, the possible equilibrium network structures can be reduced drastically and the outcomes are either symmetric or close-to-symmetric equilibrium networks. We show that the difference of social contacts among overall individuals is no greater than one contact in the close-to-symmetric equilibrium networks.