An example apparatus includes means for identifying a pattern in first cookies received via the Internet and stored in a storage device, the first cookies corresponding to devices accessing media via the Internet, means for determining an error between a first demographic estimate based on a potential pattern in the first cookies and a second demographic estimate based on user identifiers corresponding to the devices and received via the Internet, the means for determining the error to determine the potential pattern to be the pattern when the error is less than a threshold, means for accessing impression information received from a database proprietor via the Internet, the impression information including second cookies, and means for identifying a subset of the second cookies that are associated with a same person based on the pattern, the means for identifying the subset to associate impressions corresponding to the identified subset with the same person.