题目：Bonus vetus OLS: A simple method for approximating international trade-cost effects using the gravity equation
作者：Scott L. Baiera, b, 1, and Jeffrey H. Bergstrandc, d, e, ,
链接：http://www.sciencedirect.com/science?_ob=ArticleURL&_udi=B6V6D-4TS6SVB-2&_user=10&_coverDate=02%2F28%2F2009&_rdoc=1&_fmt=high&_orig=gateway&_origin=gateway&_sort=d&_docanchor=&view=c&_acct=C000050221&_version=1&_urlVersion=0&_userid=10&md5=b270957e9f5e199d756dd90c13552e26&searchtype=a