PRODUCT VARIETY AND COMPETITION IN THE RETAIL MARKET FOR EYEGLASSES*
利用美国眼镜零售商数据，研究发现本地竞争程度影响产品种类选择：随着竞争对手增多，每家店的产品种类先增后减，体现了商业窃取与集聚效应的权衡。
ABSTRACT I use original data on eyewear retailers in a cross‐section of U.S. markets to study how firms' product range choices vary with the degree of local competition. Market level regressions show average per firm variety declining in the number of rivals. In regressions at the firm level, taking account of spatial differentiation within each market, a non‐monotonic relationship between product ranges and competition is apparent. As the number of nearby rivals increases, per firm variety may first rise before eventually declining. Explanations for this pattern are offered, in terms of a tradeoff between business stealing and clustering effects.