How to Define Searching Sessions on Web Search Engines

We investigate three methods for defining a session on Web search engines. We examine 2,465,145 interactions from 534,507 Web searchers. We compare defining sessions using: 1) Internet Protocol address and cookie; 2) Internet Protocol address, cookie, and a temporal limit on intrasession interactions; and 3) Internet Protocol address, cookie, and query reformulation patterns. Research results shows that defining sessions by query reformulation along with Internet Protocol address and cookie, provides the best measure, resulting in an 82% increase in the number of sessions. Regardless of the method, mean session length was fewer than three queries and the mean session duration was less than 30 minutes. Implications are that unique sessions may be a better indicator than the common industry metric of unique visitors for measuring search traffic. Results of this research may lead to tools to better support Web searching.