There are two versions of the ‘People’ metric.
For members of the Device Co-op that do not use Cross-Device analytics, the ‘People’ metric is a statistically-derived count of the number of people represented in the report. It is the number of visitor IDs that are identified by the Device Co-op plus the number of devices that are not identified by the Co-op.
Within a Cross-Device analytics virtual report suite, the ‘People’ metric is a not a statistical derivation. Instead, it is the sum of individuals who are identified in the report, plus the number of devices that are not identified as belonging to a person.