The Gravity of Knowledge
分析跨国公司的国际运营，衡量知识转移的空间障碍，发现非物化知识转移成本是导致跨国公司子公司销售额随距离下降的主要因素。
We analyze the international operations of multinational firms to measure the spatial barriers to transferring knowledge. We model firms that can transfer bits of knowledge to their foreign affiliates in either embodied (traded intermediates) or disembodied form (direct communication). The model shows how knowledge transfer costs can be inferred from multinationals' operations. We use firm-level data on the trade and sales of US multinationals to confirm the model's predictions. Disembodied knowledge transfer costs not only make the standard multinational firm model consistent with the fact that affiliate sales fall in distance but quantitatively accounts for much of the gravity in multinational activity.