Methods and apparatus to detect carrying of a portable audience measurement device

1. A portable audience measurement device, comprising:

a housing;

a media detector in the housing to collect media exposure data;

a hinge including a hinge pin and having an arm to rotate in response to an applied force, the arm to secure the housing to an object associated with a person;

a rotation sensor to detect a magnitude of rotation of the arm relative to the housing, wherein the rotation sensor is coupled to the hinge pin, the rotation sensor including a rotary indicator to indicate the magnitude of rotation of the arm; and

a detector to compare the magnitude of rotation of the arm to a threshold angle to determine whether the device is being carried by the person.

2. The portable device as defined in claim 1 , wherein the rotation sensor includes a light source and a photodetector, wherein the photodetector is to sense light conveyed from the light source through a pattern disc onto the photodetector.

3. The portable device as defined in claim 1 , wherein the detector is to determine a likelihood that the device is being carried based on the comparison of the threshold angle and the magnitude of rotation of the arm.

4. The portable device as defined in claim 3 , wherein the detector is to credit the media exposure data based on the likelihood.

5. The portable device as defined in claim 3 , wherein the likelihood includes a primary likelihood based on information gathered by the rotation sensor, wherein the detector is to adjust the primary likelihood based on an output of a secondary sensor indicative of a position of the arm.

6. The portable device as defined in claim 5 , wherein the secondary sensor includes a contact sensor to detect a closure of the arm.

7. A method of detecting wearing of a portable audience measurement device, comprising:

detecting, using a rotation sensor coupled to a hinge pin, a magnitude of rotation of an arm associated with the hinge pin, the rotation sensor including a rotary indicator to indicate the magnitude of rotation of the arm;

determining, via a logic circuit, whether the magnitude of rotation is indicative of the device being worn by a person based on a comparison of the magnitude of rotation of the arm to a threshold angle; and

calculating, via the logic circuit, a likelihood that the device is being worn by the person based on a result of the comparison.

8. The method as defined in claim 7 , wherein calculating the likelihood includes calculating a frequency of indications that the device is being worn by the person for a period of time.

9. The method as defined in claim 7 , further including generating a message of non-compliance in response to determining that the likelihood is lower than a threshold likelihood.

10. The method as defined in claim 7 , further including comparing a time of a last detected actuation of the hinge to a threshold amount of time in response to determining that the device is not being worn by the person.

11. The method as defined in claim 10 , wherein a change in a status of the hinge as detected by the rotation sensor indicates actuation of the hinge by the person.

12. The method as defined in claim 10 , further including generating a message of non-compliance in response to determining that the time is greater than the threshold amount of time.

13. The method as defined in claim 7 , further including using the likelihood to determine whether collected media exposure information is to be credited.

14. The method as defined in claim 7 , further including conveying the calculated likelihood to a central facility.

15. A tangible computing readable storage device or storage disc comprising instructions that, when executed, cause a machine to at least:

detect a magnitude of rotation of an arm of a hinge of a portable device with a rotational sensor coupled to a hinge pin of the hinge, the rotation sensor including a rotary indicator to indicate the magnitude of rotation of the arm;

determine whether the magnitude of rotation is indicative of the portable device being worn by a person based on a comparison of the magnitude of rotation of the arm to a threshold angle; and

calculate a likelihood that the device is being worn by the person based on a result of the comparison.

16. The storage device or storage disc as defined in claim 15 , wherein the instructions, when executed, cause the machine to calculate the likelihood by calculating a frequency of indications that the device is being worn by the person for a period of time.

17. The storage device or storage disc as defined in claim 15 , wherein the instructions, when executed, cause the machine to generate a message of non-compliance in response to determining that the likelihood is lower than a threshold likelihood.

18. The storage device or storage disc as defined in claim 15 , wherein the instructions, when executed, cause the machine to compare a time of a last detected actuation of the hinge to a threshold amount of time in response to determining that the arm is in a position indicating that the device is not being worn by the person.

19. The storage device or storage disc as defined in claim 18 , wherein the instructions, when executed, cause the machine to generate a message of non-compliance in response to determining that the time is greater than the threshold amount of time.

20. The storage device or storage disc as defined in claim 15 , wherein the instructions, when executed, cause the machine to use the likelihood to determine whether collected media exposure information is to be credited to the person.

21. The storage device or storage disc as defined in claim 15 , wherein the instructions, when executed, cause the machine to convey the calculated likelihood to a central facility.