How do they measure how many people listen to a particular radio station?

Question

do they guess, do a survey, or is there a technological way they do it? for example, when they say a radio show has 10,000 listeners - how do they know that?

Answer 1

In the US, there are a few companies out that perform surveys of radio listeners.

In most markets, they send a small number of people who have accepted a invitation a log book to write down what they listened to that week (a sample group). at the end of the week it's returned and in a month or two, the radio station gets a report of that sampling, say that 5 % of the listening audience was tuned into your program.

The law of averages take over, in that if we sample 1% of the general populance, they should be able to give me ideas on the listening habits of the other 99%

In some markets such as Houston,Tx. they have moved from the diaries to what are called personal people meters.. this is a pager like device that samples what is being played and ultimately can be decoded into what the person was actually hearing as the diaries didn't take into account say walking in a mall, or people who don't like to fill out diaries (such as young white males) and gives a more accurate picture.

http://en.wikipedia.org/wiki/Arbitron