text: Media usage used to be tracked through market research and consumer surveys/census using a special set top box attached to the TV. This device tracks what channels a typical household watches.  The survey contains the ages of the viewers and the time each of them watches TV.  And this device is kept for months in surveyed households.  Nowadays, with cable TV, monitoring is much more difficult.  Not only that, even music is no longer exclusively heard through radio, you have CDs, mp3s and a whole lot more variety of media choices.  How do you track media usage with all this information?  Internet surveys is one way.  But these are difficult to validate without the devices that attest that one watches specific shows at specific times.  Can you safely presume that everyone answers the survey correctly and honestly?  This is one great challenge of market research today.