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Lesson 8-7
Using Sampling to Predict
Definitions• Sample - A small group, it is
representative of a larger group, called a population.
Definitions• Unbiased sample - selected so that it is
representative of the entire population.
Type Definition Example
Simple Random Sample
A sample where each item or person in the population is as likely to be chosen as any other.
The names of all students are put into a hat and drawn blindly.
Stratified Random Sample
The population is divided into similar, non-overlapping groups. A simple random sample is then selected from each group.
Students are picked at random from each grade level at a school.
Systematic Random Sample
The item or people are selected according to a specific time or item interval.
From an alphabetical list of all students attending a school, every 20th person is chosen.
Definitions• Biased sample - One or more parts of a
population are favored over others.
Type Definition Example
Convenience Sample
A convenience sample includes members of a population that are easily accessed.
To represent all students in the school, the principal surveys one math class.
Voluntary Response Sample
A voluntary Response Sample involves only those who want to participate in the sampling.
Students at a school who wish to express their opinion are asked to come to the office after school.
To determine which school lunches students like most, every twentieth student to walk into the cafeteria is surveyed.
Describe each sample
To determine what sports teenagers like, the student athletes on the girls’ field hockey team are surveyed.
Unbiased – systematic random sample
Biased – convenience sample
BOOKS: The student council is trying to decide what types of books to sell at its annual book fair to help raise money for the eighth-grade trip. It surveys 40 students at random. The books they prefer are in the table.
Book Types Number of
Students
Mystery 12
Adventure Novel
9
Sports 11
Short Stories 8
What percent of the students prefer mysteries?
If 220 books are to be sold at the book fair, how many should be mysteries?
