Methods and apparatus to adjust signature matching results for audience measurement

1. A method to adjust a signature matching result associated with monitoring a media presentation, the method comprising:

obtaining a monitored signature representative of the monitored media presentation from a monitoring device;

obtaining an environmental characteristic associated with the monitored signature from the monitoring device; and

adjusting the signature matching result using an adjustment value when the monitored signature is determined to match a reference signature representative of reference media, the adjustment value selected from a plurality of adjustment values based on the matched reference signature and the environmental characteristic, wherein the monitored signature includes a video signature, and the environmental characteristic includes at least one of a brightness level or an ambient light level measured by the monitoring device.

2. A method as defined in claim 1 wherein the signature matching result is representative of a number of times monitored signatures obtained from the monitoring device are determined to match corresponding reference signatures representative of the reference media.

3. A method as defined in claim 1 wherein the environmental characteristic further includes information descriptive of at least one of the monitoring device or a configuration of the monitoring device.

4. A method as defined in claim 1 wherein the environmental characteristic further includes information descriptive of at least one of a media device presenting the monitored media presentation or a configuration of the media device.

5. A method as defined in claim 1 wherein adjusting the signature matching result comprises scaling the signature matching result by the adjustment value.

6. A method as defined in claim 1 further comprising selecting the adjustment value from a set of adjustment values associated with at least one of the reference signature or the reference media, each adjustment value in the set of adjustment values associated with one or a combination of environmental characteristics.

7. A method as defined in claim 1 further comprising:

storing the adjusted signature matching result in memory; and

retrieving the stored adjusted signature matching result from the memory for comparison with a threshold to determine whether to credit the monitored media presentation as corresponding to the reference media.

8. A method as defined in claim 1 further comprising:

presenting the reference media in a controlled environment having a first configuration setting from a plurality of possible configuration settings;

determining a set of test signatures by monitoring the presentation of the reference media in the controlled environment;

counting a number of successful matches between the set of test signatures and a respective set of reference signatures representative of the reference media to determine the adjustment value; and

storing the adjustment value in memory for subsequent selection to adjust the signature matching result, the adjustment value to be selected when the environmental characteristic corresponds to the first configuration setting.

9. A method as defined in claim 8 wherein the first configuration setting corresponds to a first brightness setting of a media device included in the controlled environment to present the reference media and a first ambient light setting of an ambient light generator included in the controlled environment.

10. A method as defined in claim 8 further comprising determining the plurality of adjustment values to correspond to a plurality of possible reference media sources and the plurality of possible configuration settings.

11. A tangible machine readable storage medium, excluding propagating signals, and comprising machine readable instructions which, when executed, cause a machine to at least:

obtain a monitored signature representative of a monitored media presentation from a monitoring device;

obtain an environmental characteristic associated with the monitored signature from the monitoring device; and

adjust a signature matching result using an adjustment value when the monitored signature is determined to match a reference signature representative of reference media, the adjustment value selected from a plurality of adjustment values based on the matched reference signature and the environmental characteristic, wherein the monitored signature includes a video signature, and the environmental characteristic includes at least one of a brightness level or an ambient light level measured by the monitoring device.

12. A storage medium as defined in claim 11 wherein the environmental characteristic further includes information descriptive of at least one of the monitoring device, a configuration of the monitoring device, a media device presenting the monitored media presentation or a configuration of the media device.

13. A storage medium as defined in claim 11 wherein the machine readable instructions, when executed, further cause the machine to:

present the reference media in a controlled environment having a first configuration setting from a plurality of possible configuration settings;

determine a set of test signatures by monitoring the presentation of the reference media in the controlled environment;

count a number of successful matches between the set of test signatures matches and a respective set of reference signatures representative of the reference media to determine the adjustment value; and

store the adjustment value in memory for subsequent selection to adjust the signature matching result, the adjustment value to be selected when the environmental characteristic corresponds to the first configuration setting.

14. An apparatus to adjust a signature matching rate associated with monitoring a media presentation, the apparatus comprising:

a signature comparator to obtain a first monitored signature representative of the monitored media presentation from a monitoring device, the signature comparator to compare the first monitored signature with a plurality of reference signatures representative of a plurality of reference media sources; and

a match rate adjuster to adjust the signature matching rate using a first adjustment value when the first monitored signature is determined to match a first reference signature representative of reference media source from the plurality of reference media sources, the signature matching rate representative of a frequency with which reference signatures representative of a first reference media source are successfully matched during a measurement time interval, the first adjustment value selected based on the matched first reference signature and a first environmental characteristic associated with first monitored signature, the first environmental characteristic obtained from the monitoring device, wherein the first monitored signature includes a video signature, and the first environmental characteristic includes at least one of a brightness level or an ambient light level measured by the monitoring device.

15. An apparatus as defined in claim 14 wherein the first environmental characteristic further includes information descriptive of at least one of the monitoring device, a configuration of the monitoring device, a media device presenting the monitored media presentation or a configuration of the media device.

16. An apparatus as defined in claim 14 wherein the match rate adjuster is to further adjust the signature matching rate using a second adjustment value when a second monitored signature obtained from the monitoring device is determined to match a second reference signature representative of a second reference media source, the second adjustment value selected based on the matched second reference signature and a second environmental characteristic associated with the second monitored signature, the second environmental characteristic obtained from the monitoring device.

17. An apparatus as defined in claim 16 wherein the first environmental characteristic corresponds to at least one of a first brightness level or a first ambient light level, and wherein the second environmental characteristic corresponds to at least one of a second brightness level or a second ambient light level.

18. An apparatus as defined in claim 14 further comprising memory to store a plurality of adjustment values corresponding to the plurality of reference signatures and to a plurality of environmental characteristics, each adjustment value associated with a particular reference signature and a particular combination of environmental characteristics.

19. An apparatus as defined in claim 14 further comprising a signature tester to:

present the first reference media source in a controlled environment having a first configuration setting from a plurality of possible configuration settings;

determine a first set of test signatures by monitoring the presentation of the first reference media source in the controlled environment;

determine a first ratio of a number of successful matches of the first set of test signatures with a respective set of reference signatures representative of the first reference media source to a total number of the first set of test signatures to determine the first adjustment value; and

store the first adjustment value in memory for subsequent selection to adjust the signature matching rate, the first adjustment value to be selected when the first environmental characteristic corresponds to the first configuration setting.

20. An apparatus as defined in claim 14 wherein the signature tester is further to:

present the first reference media source in the controlled environment having a second configuration setting from the plurality of possible configuration settings;

determine a second set of test signatures by monitoring the presentation of the first reference media source in the controlled environment;

determine a second ratio of a number of successful matches of the second set of test signatures matches with the respective set of reference signatures representative of the first reference media source to a total size of the second set of test signatures to determine a second adjustment value; and

scale the first adjustment value by the second adjustment value before storing the first adjustment value in memory.