The authors quantify revenue loss from several sources, including the direct effects of charging for part of the online content and the reduced effectiveness of search-engine referrals and e-mails.

• 作者对收入损失的原因进行了量化，包括对在线内容的部分收费的直接影响、搜索引擎推荐和电子邮箱的效果的减弱。