I once participated in data gathering for Arbitron, which gathers radio stats.

It was very simple. For some period of time (I think it was a week...this was a long time ago so details are fuzzy) I was supposed to write down the time and identity of every radio station I heard (or maybe every station I heard for more than a few minutes?). At the end of the survey period, I mailed that to them.

I forget how much they paid, but I think it was on the order of a few dollars.

This would have been quite a while ago--probably at least 20 years ago.

They still do that kind of survey, I believe, a few times a year in each of several hundred metropolitan areas.

In 2007, they added another data gathering method that they use in a smaller number of major markets where participants wear a small device that can pick up subaudible identification messages embedded in radio broadcasts to tell what radio stations are being played in an area. These devices record that information and periodically send the data back to the company.

In 2012 they were bought by Neilsen and are now called Neilsen Audio, but the data gathering is still as described above.

Last I checked it was way more low tech than you’d expect for a company people put a lot of stock in. Basically, they put scanners on some people’s TV’s (with their permission, which is good but introduces a lot of selection bias) and try to correlate what gets watched with the ages of the people in the house (while not knowing whos watching what and hoping the TV doesn’t just get left on for hours with no one watching).

They give you a remote with toggle buttons labeled with people's names so you can tell it who is watching or if multiple people are watching. They also have software for media pcs but you can hook up an intermediary box if you want. They also pay you per hooked up tv, and have stats on whether a tv is a bedroom / kitchen / family room tv.

You get a black tracking box installed at your house.

TV-tracking is done by sound signatures and web-tracking is done with a router which has custom firmware installed.

At least at one point, Nielsen were getting their stats by paying people to install their iOS monitoring app using an enterprise developer certificate: http://www.arbitron.com/research/installhelp/install_ios9_en... Including minors as young as 13 with parental consent: http://www.arbitron.com/research/faq/iBoard_faq_en.pdf