Campbell Live's future depends on ratings. But how do they work?

Six-hundred Kiwi households have people-meters, which TVNZ says equates to around 1500 individuals. Photo / Thinkstock

In television it's often said you live or die by the ratings. But just who is watching what we're watching?

In New Zealand, like most other Western countries, ratings are determined by electronic meters, known as people-meters. The meters record who is watching what, and when.

The data is transmitted back to research company AGB Nielsen each night around 2am.

Six-hundred Kiwi households have people-meters, which TVNZ says equates to around 1500 individuals.

Those individuals make up the people-meter panel, which is specifically chosen to reflect the population of New Zealand, based on data from the Census. Each household can remain on the panel for up to six years.

In 2012, Nielsen introduced new technology, allowing it to monitor time-shifted viewing, such as programmes recorded on MySky and watched at a later date.

Nielsen says the people-meter system is recognised as global best practice.

TVNZ, MediaWorks and Sky all subscribe to Nielsen's system although Sky admits it also has an internal set-top-box audience measurement system in place.

Data from that system is not distributed and is used for internal purposes only.

But though some question the effectiveness of the system, which uses data from just 0.014 per cent of the population to represent the whole country's viewing habits, TVNZ says it has full confidence in it.

"It's a well-established process, not just in New Zealand, but around the world," says Jonathan Symons, general manager of data and insights.

"It takes account of all broadcast viewing, including how households that have digital recorders record programmes and watch them later.

"Measuring viewing continuously, rather than just occasional surveys, provides information that can be tracked over time and improves confidence significantly."

He says TVNZ is in discussions with Nielsen about what future measurement may look like but says the panel-based approach will continue and form the core of the measurement process.