Internet search engines display advertisements along with search results, providing them with a major source of revenue. The display of ads is triggered by the use of keywords, which are found in the searches performed by search engine users. The fact that advertisers can buy a keyword that contains a trademark they do not own has caused controversy worldwide. To explore the actual effects of trademark and keyword advertising policies, we exploit a natural experiment in Europe. Following a decision by the Court of Justice of the European Union, Google relaxed its AdWords policy in continental Europe in September 2010. After the policy change, Google allowed advertisers to select a third party's trademark as a keyword to trigger the display of ads, with only a limited complaint procedure for trademark owners. We use click-stream data from European Internet users to explore the effect this policy change had on browsing behavior. Based on a data set of 5.38 million website visits before and after the policy change, we find little average change. However, we present evidence that this lack of average effect stems from an aggregation of two opposing effects. While navigational searches are less likely to lead to the trademark owner's website, non-navigational searches are more likely to lead to the trademark owner's website after the policy change. The effect of changing keyword advertising policies varies with the purpose of the consumers using the trademark, and it is more pronounced for lesser-known trademarks. The article points to tradeoffs trademark policy is facing beyond consumer confusion. More generally, the article proposes a novel way of analyzing the effect of different allocations of property rights in intellectual property law
