In the middle of all of this is a new breed of research corporation that relies on you – the survey taker – to determine this information. For your time? Many survey companies will pay you to take surveys for money or for other cash alternatives like gift cards or physical prizes and rewards. It depends upon the company as to whether they'll offer money or other offers and special deals.
Global Test Market is a decent standard of what you're getting yourself involved in. Their practices are not any more or less shady or reputable than almost any online venue – survey or otherwise. Just like Facebook, when you identify yourself accurately with Global Test Market, you can expect them to use that information in any way possible to make a penny. The great news is they inform you and ask for consent first.