(The  industrial concentration) is based upon the 5 firm domestic concentration ratio based upon output, i.e., the proportion of output accounted for by the largest 5 firms.  It has been modified to include the impact of imports on competition, so that the crude ratio has been multiplied by (1-m) where m is the ratio of imports to total sales.
不是特别理解为什么要乘(1-m) ,哪位高人请帮我分析一下?
万分感谢!