Methods and apparatus to correct audience measurement data

A non-transitory computer readable storage medium comprising instructions that, when executed, cause at least one processor to at least:

• access a unique audience size of database proprietor subscribers exposed to media, the unique audience size of the database proprietor subscribers generated by a process of a server of a database proprietor based on a first quantity of impressions, the first quantity of impressions corresponding to first client devices that include database proprietor identifiers, the first quantity of impressions exclusive of a second quantity of impressions corresponding to second client devices that do not include the database proprietor identifiers;
• and
• apply a missing-audience factor to the unique audience size of the database proprietor subscribers exposed to the media to produce a coverage-corrected unique audience size that corrects the unique audience size generated by the server of the database proprietor by using the coverage-corrected unique audience size to represent the first and second client devices in place of the unique audience size that corresponds to the first client devices exclusive of the second client devices.

A method comprising:

• accessing, by executing an instruction with a processor, a unique audience size of database proprietor subscribers exposed to media, the unique audience size of the database proprietor subscribers generated by a process of a server of a database proprietor based on a first quantity of impressions, the first quantity of impressions corresponding to first client devices that include database proprietor identifiers, the first quantity of impressions exclusive of a second quantity of impressions corresponding to second client devices that do not include the database proprietor identifiers;
• and
• applying, by executing an instruction with the processor, a missing-audience factor to the unique audience size of the database proprietor subscribers exposed to the media to produce a coverage-corrected unique audience size that corrects the unique audience size generated by the server of the database proprietor by using the coverage-corrected unique audience size to represent the first and second client devices in place of the unique audience size that corresponds to the first client devices exclusive of the second client devices.