Disclosed examples obtain an overlap multiplier as a ratio of (1) a first product of a panel duplication reach and a did-not-view reach and (2) a second product of a television panel reach and a digital panel reach, the panel duplication reach based on a duplicated audience size and a panelist population, the did-not-view reach based on a television audience size, a digital audience size, the duplicated audience size, and the panelist population, the television panel reach corresponding to the television audience size, the digital panel reach corresponding to the digital audience size; and determine a total audience for a media item based on a television audience reach, a digital audience reach, and a duplication factor, the duplication factor based on the television audience reach, the digital audience reach, and the overlap multiplier, the television audience reach corresponding to television media, the digital audience reach corresponding to digital media.