Sampling Methods
Systematic
A lobby has a list of 100 senators of the United States. In order to determine the Senate's position regarding farm subsidies, they decide to talk with every seventh senator on the list starting with the third.
Voluntary Response
A radio station asks its listeners to call in their opinion regarding the use of American forces in peacekeeping missions.
Stratified
A school official divides the student population into five classes: freshman, sophomore, junior, senior, and graduate student. The official takes a random sample from each class and asks the members' opinions regarding student services.
Cluster
A farmer divides his orchard into 50 subsections, randomly selects 4 and samples all of the trees within the 4 subsections in order to approximate the yield of his orchard.
Voluntary Response
A survey regarding download time on a certain Web site is administered on the Internet by a market research firm to anyone who would like to take it.
Simple Random Sample
A teacher wants to select 5 students to present their projects on the first day so she puts all 25 students names in a hat and randomly draws 5 names.
Cluster
In an effort to determine customer satisfaction, United Airlines randomly selects 50 flights during a certain week and surveys all passengers on the flights.
Convenience
In an effort to identify whether an advertising campaign has been effective, a marketing firm conducts a nationwide poll by randomly selecting individuals from a list of known users of the product.
Cluster
In order to determine the average IQ of ninth-grade students, a school psychologist obtains a list of all schools in the local public school system. She randomly selects five of these schools and administers an IQ test to all ninth-grade students at the selected schools.
Systematic
In order to estimate the percentage of defects in a recent manufacturing batch, a quality control manager at Intel selects every 8th chip that comes off the assembly line starting with the 3rd, until she obtains a sample of 140 chips.
Simple Random Sample
A marketing company wants to determine how satisfied NBA players are with their agents, so they get a list of all current players and randomly select 50 to survey.
Stratified
A member of Congress wishes to determine her constituency's opinion regarding estate taxes. She divides her constituency into three income classes: low-income households, middle-income households, and upper-income households. She then takes a random sample of households from each income class.