US Patent 9154565 Methods and apparatus to monitor online activity

An example method to monitor online activity involves comparing first uniform resource locators collected from a first client device of a known panelist with second uniform resource locators collected from second client devices associated with different users; and determining which of the second uniform resource locators correspond to online activity of the known panelist based on ones of the first uniform resource locators matching at least portions of ones of the second uniform resource locators.