• Watch an episode of a program, and then
• Chose not to watch a subsequent episode of the same program when given an opportunity to do so, but watch a competing program at the same time.

Defection charts, and the closely related program loyalty charts, are powerful tools for gauging the strength of programs, particularly new programs. They show the number of people who watched a program, and decided to watch something else the next time it was aired.

For programs that will eventually fail, defection numbers will often indicate failure long before rating and share values begin dropping.

Note: A person is not considered to be a defector if he or she watches an episode, and then does not watch television when a subsequent episode is being aired. Mowing the lawn while a program is airing is not an indicator of defection. Defection occurs only when the person has an opportunity to watch an episode, but chooses not to watch by selecting a competing program.

News Defection

Reading a defection chart requires a little practice. In the chart above, we see that:

• Blue line first point Of the people who watched News #13 on week 1 and were watching television at 9:08 PM on week 2, 78% were not watching News #13.
• Blue line second point Of the people who watched News #13 on week 1 and were watching television at 9:08 PM on week 3, 68% were not watching News #13.
• Red line first point Of the people who did not watch News #13 on week 1 but did watch News #13 on week 2, and were watching television at 9:08 PM on week 3, 79% did not watch News #13.