Identify the kind of sample that is described:

1. Website ratings: A popular website is interested in conducting a survey of 400 visitors to the site in such a way that 200 of them will be under age 30, 150 will be aged 30-55, and 50 will be over 55.
2. Favorite performer: Viewers of a television show are asked to vote for their favorite performer by sending a text message to the show.
3. School days: A researcher selects 4 of 12 high schools in a certain region and surveys all of the administrative staff members in each school about a potential change in the ordering of supplies.
4. Political polling: A pollster obtains a list of registered voters and uses a computer random number generator to choose 100 of them to ask which candidate they prefer in an upcoming election.