Methods and apparatus to adjust signature matching results for audience measurement are disclosed. An example method to adjust a signature matching result associated with monitoring a media presentation disclosed herein comprises obtaining, from a monitoring device, an audio signature representative of the monitored media presentation, obtaining, from the monitoring device, an environmental characteristic associated with the audio signature, and adjusting the signature matching result using an adjustment value when the audio signature is determined to match a reference signature representative of reference media, the adjustment value being selected from a plurality of adjustment values based on the matched reference signature and the environmental characteristic.