In the old days the Nielsen ratings of TVwatching habits wou

In the old days, the Nielsen ratings of TV-watching habits would ask people to fill out a card indicating how much TV they watched and which shows they watched. Why did they get different results when they used electronic monitoring devices instead?

Solution

when using electronic devices different results are because they handle better accuracy, as they are completely automated controls that are installed in homes sample and measuring the number of hours of each program being viewed and the amount of daily people who see it, whereas when filling a form (card) may be passed unnoticed any data.