The truth is we can never know for definite how many people were watching TV last night, but we have ways of estimating it very accurately. The television broadcasters jointly run a survey of more than 5000 households across the UK, monitoring what they watch. In the old days this consisted of relying on people in selected households to tell us what they watched by filling in a paper survey. Now we have small electronic boxes that attach to the back of people's TV sets, throughout the house, which records who's watching what and when. The when is very important here - because we now have to monitor when people are watching pre-recorded TV too.
In the middle of the night, each of these boxes sends this information for processing and by the next morning we know what people were watching the night before. A second set of data is available a fortnight later which collects information from viewing of catch-up channels and pre-recorded programmes. You can find out more information about the process from BARB.
Measuring who's listened to what on radio is a longer process. We mainly rely on people's recall of what they have been listening to. As with TV, the radio industry works together to run a survey to collect the nation's listening habits. This produces results once every three months. You can read the most recent figures here. Each year more than 100,000 people report back what they have been listening to - find out more from Rajar. This now includes listening through DAB radios, TVs, mobiles and other newer methods. We have started publishing our online radio listening figures.
Tracking how often people visit us online and on mobile is a developing area of measurement. Activity on these platforms is more frenetic than traditional TV watching and radio listening; URLs change, computers don't always keep the same unique identifier, individuals access the internet from lots of different places. But these measurements are becoming more sophisticated and there is a lot that we do know. We know that over the election xxxx pages were viewed. We also know that there were over 25 million requests to watch or listen to programmes on iPlayer last week. We publish our iPlayer usage statistics monthly.
We often now have to combine lots of these measurements - for example, to find out how many people watched Doctor Who on the weekend is an amalgamation of live and recorded TV viewing, as well as online viewing. And to find out how many people access any BBC service we have developed a survey that looks at BBC usage across all platforms.
And how many people were watching TV last night? Our survey says xxm.
Jo Hamilton is Head Of Audience Measurement
