EPI/ BISTATS: SAMPLING METHODS
The police set up checkpoints at randomly selected road locations, then inspected every driver at those locations.
Cluster random sample
A store prints a request on each receipt asking customers to fill out a satisfaction survey online if they are willing.
not random: voluntary
A hospital wants to survey religious participants in their city about what they seek from a hospital chaplain, so they randomly select 5 religious meetings in the city and survey every participant in those meetings.
Cluster random sample
A principal orders t-shirts and wants to check some of them to make sure they were printed properly. She randomly selects 2 of the 10 boxes of shirts and checks every shirt in those 2 boxes.
Cluster random sample
Simple random sample
Each student at a school has a student identification number. Counselors have a computer generate 50 random identification numbers, and the students associated with those numbers are asked to take a survey.
A politician asks his neighbors their opinions about a controversial issue.
Not random: Convenience
A researcher polls people as they walk by on the street.
Not random: Convenience
A support hotline asks callers to stay on the line after they have completed their call to respond to a short survey.
Not random: Voluntary
A concert venue offers tickets in 3 zones: orchestra, grand tier, and balcony. Tickets in the orchestra zone are most expensive, and tickets in the balcony zone are least expensive. Managers of the venue want to survey approximately 150 guests at an upcoming concert about their overall experience. They want to take a stratified random sample of guests based on the venue's zones.
Randomly select 50 tickets from each zone and invite those guests to participate in the survey.
A manager associated each employee's name with a number on one ball in a container, then drew balls without looking to select a sample of 5 employees.
Simple random sample
A teacher puts students names in a hat and chooses without looking to get a sample of 3 students.
Simple random sample
Each law firm in one state registers its phone number with the state court system. An employee of the state court system uses a computer to select 500 random registered phone numbers, and the law firms associated with those numbers will be selected for an audit.
Simple random sample
A large company surveys 100 employees by taking random samples of 10 managers and 90 non-managerial employees.
Stratified random sample
A school chooses 3 randomly selected athletes from each of its sports teams to participate in a survey about athletics at the school.
Stratified random sample
A truck manufacturer selects 3 trucks at random from each of 6 models for safety testing.
Stratified random sample
A professor asks the first 5 students who arrive to class to participate in a research study about young adult sleep patterns.
Not random: convenience
A student council surveys 100 students by taking random samples of 25 freshmen, 25 sophomores, 25 juniors, and 25 seniors.
stratified random sample