From the 1980s until relatively recently, most national polling organizations conducted surveys by telephone, relying on live interviewers to call randomly selected Americans across the country. Then came the internet.
It has taken survey researchers some time to adapt to the idea of online surveys, but a quick look at the public polls on an issue like presidential approval reveals a landscape now dominated by online polls rather than phone polls. Pew Research Center itself now conducts the majority of its U.S. polling online, primarily through its American Trends Panel. CONT.
Courtney Kennedy & Claudia Deane, Pew