Sampling Method
Stratified Random Sample
After the population is divided into groups (called strata), a probability sample is selected within each group. The sample includes elements from each group
Convenience Sample
Astroducks Coffee House wants to know how much caffeine college students drink in a day. Astroducks sends a survey out to the college that is closest to their headquarters in Carlsbad
Systematic Random Sample
Cardiff Kook Academy wants to examine the college and career goals of the students. Each student is assigned a random number. A random digit between 0 and 9 is selected to represent the first student to be surveyed and then every 20th student after that is surveyed.
Convenience Sample
Student organization looking to get signatures for a petition camp out in front of class of 1950 Lecture Hall.
Experiment
To determine if a new pain medication is effective, researchers randomly assign people into two groups: group 1 receives pain medications and group 2 receives a placebo. Both groups are asked to rate their pain and the results are compared. (survey, observational study, or experiment)
Survey
To determine if a new sandwich on the menu is liked more than the original, the manager of the restaurant takes a random sample of customers that have tried both sandwiches and asks them which sandwich they prefer. (survey, observational study, or experiment)
Simple Random Sample
When all possible samples are equally likely to occur
Stratified Random Sample
A company is investigating differences in income for various ethnicities. The company chooses to randomly survey 500 people in each of the designated ethnicities.
Volunteer Sample
A company wants to know how much time the population spends on answering emails in a given day. They post a link on their website asking for people to take an online survey.
Simple Random Sample
A group of 25 employees are chosen out of a hat from a company of 250 employees
Survey
A newspaper wants to know what their customer satisfaction is. They randomly select 500 customers and ask them (survey, observational study, or experiment)
Cluster Random Sample
A researcher is studying the education levels of the population of Spain. The researcher randomly selects 20 cities in Spain and surveys every person in those cities
Convenience Sample
A sample made up of people who are easy to reach
Volunteer Sample
A sample made up of people who self-select into the survey. These people often have a strong interest in the topic of the survey
Convenience Sample
Priceline.com randomly e-mails a customer satisfaction survey for certain transactions done on its site in which customers choose to either respond or not.
Parameter
Question you want to know about a population
Stratified Random Sample
Divide the class knot four groups (freshman, sophomore, junior, and senior) and take a random sample of two students from each group.
Stratified Random Sample
Elvira assigns every student in the school a number and randomly selects 60 students to survey to determine if students at the school are satisfied with school lunch
Cluster Random Sample
Elvira randomly selects 7 different tables in the lunch room and surveys every student at the table to determine if students at the school are satisfied with school lunch
Systematic Random Sample
Elvira selects every 5th student in the lunch line to determine if students at the school are satisfied with school lunch
Convenience Sample
Elvira surveys the first 60 students in the lunch line to determine if students at the school are satisfied with school lunch
Volunteer Sample
Elvira wants to determine if students are satisfied with school lunch. She leaves surveys in a table for students to answer as the walk by
Population
Entire group
Systematic Random Sample
From a list of every member of the population, we select the first sample element from the first k elements on the list, and then select every kth element
Convenience Sample
In Fall 1995, the BBC in Britain requested viewers to call the network and indicate their favorite poem.
Sample
Number, group selected to represent
Cluster Random Sample
After the population is assigned to one group (called a cluster), a sample of clusters is randomly chosen. The sample includes only those within sample includes only those within sampled clusters
Observational Study
Officials want to determine if raising the speed limit from 75 mph to 80 mph will have an impact on safety. To determine this, they watch a stretch of the highway when the speed limit is 75 and see how many accidents there are. Then they observe the number of accidents over a period of time on the same stretch of highway for a speed limit of 80mph. Then they compare the difference. (survey, observational study, or experiment)
Stratified Random Sampling
Select three female students and three make students to receive ice cream by putting all the men's names in one hat and all the women's names in a different hat and picking out three names from each hat.
Simple Random Sample
Select three students from a class to receive ice cream by putting all the students' names in a hat and picking out three names randomly.
