Controlled variable = Elements that you keep the same. The offer, images, and ad text would would be kept identical. I just pick an image I did well, used “Game of the Year 2008″, and there was only one offer to choose from.
Independent variable = What am I changing or testing? I’m testing the age groups.
Dependent variable = The new value that changes. Basically I’m looking at the click-through rates, cpc’s, and the return on investment.