Quiz's are popular and engage the users. Here is the WWF that tries to create interest and provide donations. And email addresses. Here, users must submit their address to participate. In other quizzes, the user just goes ahead and must finally submit the e-mail address to get the result. WWF's method is the most honest, but it is possible that the second method is more effective. People will not have wasted their time on a quiz if they do not get the result and will therefore feel compelled to submit their email. But may be a little annoyed.