SAMPLING METHODS UNIT QUESTION: How do you use probability to make plans and predict for the future? Today’s Question: How do we take a random sample, and what statistics can we find with the data?

1.Survey 2.Population 3.Sample 4.Random Sample 5.Stratified Random Sample 6.Systematic Sample 7.Convenience Sample 8.Voluntary Sample 9.Representative Sample 10. Biased Sample 11. Biased Question

A study of one or more characteristics of a group.

The entire group you want information about.

A smaller part of the population.

When every member of the population has an equal chance of being chosen. Example: The name of each student is written on paper and placed in a bowl where names are picked without looking.

After the population is divided into distinct groups, members of the sample are selected at random from each group. Example: Students are picked at random from each grade level at a school.

Members of the population are picked according to a specific time or interval. Example: From an alphabetical list of all students, every 20 th person is chosen.

Divide the population into groups (called clusters), randomly select some of the groups, and then collect data from ALL members of the selected groups

Easily accessible members of the population are picked for the sample. Example: To represent all students at a school, the principal surveys the students in one math class.

When the sample is made up volunteers from the population. Example: Students at a school who wish to express their opinion are asked to come to the office after school. (a.k.a., Self-Selected Sample)

A sample that accurately reflects the characteristics of the population. Example: To determine what videos their customers like, every tenth person to walk into the video store is surveyed. (e.g., simple random, stratified, systematic, and cluster sample)

A sample that does NOT reflect the characteristics of the entire population; one or more parts of the population are favored over others. (e.g., convenience sample and voluntary sample) Example: To determine what people like to do in their spare time, patrons of a movie theater are surveyed.

A television reporter interviewed travelers stranded at an airport during a snowstorm about the efficiency of air travel in Canada.

A soap company distributed free samples of a new laundry detergent to all households in four randomly selected neighborhoods in Douglasville.

A psychologist is studying the sleep patterns of 3750 students at a university. She assigns each student a number between 1 and She selects the sample by randomly choosing every 50 th number.

A psychologist is studying the sleep patterns of 3750 students at a university. 30 students are randomly selected from the College of Liberal Arts, College of Fine Arts, College of Engineering, College of Medicine, and College of Law.

A question that encourages a particular response. Example: Should the lunch menu offer baked chicken since fried foods are unhealthy?

Representative

Random Samples Stratified Random Samples

Convenience Samples Self-Selected Samples

A management company wants to gather information about tenant satisfaction with the condition of their apartments. They survey 40 random tenants from each apartment building.

A bicycling club wants to gather information about biking conditions throughout the city. A survey for bicycle riders is posted on the club’s website.

Because there is a lack of affordable entertainment for teenagers in the city, do you think the city should sponsor more youth activities? Do you think the city should sponsor more youth activities?

Do you think the city should risk an increase in taxes by allowing a new elementary school to be built? Do you think a new elementary school should be built?

I want to know the average age of students at McEachern High School. What would be a good method to find this number without checking every student?

John surveys every fifth person leaving a pet supply store. Of those surveyed, ¾ support the city manager’s proposition to tear down the old library and replace the area with the construction of a new pet park. John plans to write a letter to the editor of the local newspaper about the proposal for the new pet park stating that there is tremendous support from the citizens of the town for constructing a new pet park. a)Can the conclusion John stated be accurately supported? b) Suggest another plan for obtaining a good sample population.