Page 191 - Math Course 3 (Book 2)

Understanding Proportions and Ratios

CONCEPT SUMMARY Unbiased Samples

Type Definition Example

Simple Random a sample where each item or person in a Thirty students are randomly selected
Sample population is as likely to be chosen as any by a computer based on Student ID
other. number.

Stratified Random a sample in which the population is divided Five students are chosen with birthdays
Sample into similar, non-overlapping groups. in the same month, for each of the 12
months.
A simple random sample is then selected
from each group.

Systematic a sample in which the items or people are Every 20 minutes a costumer is chosen.
Random Sample selected according to a specific time or or
item interval. Every 10th costumer in line is chosen.

Convenience a sample which includes members of the City council surveys residents within
Sample population that are easily accessed. 1-mile of a park whether to add a
recreation center to the park.

Voluntary a sample which involves only those who The school board sent an email to
Response Sample want to participate in the sampling. graduating seniors asking them where
to hold commencement. Senior are
asked to vote through an online poll.

Let’s Begin

Identify and Describe Samples

Example

Mr. Ackerman needs several volunteers to collect A hardware store wants feedback on their prod-
homework before each class. He randomly calls ucts and service. They include a telephone num-
out a color and whoever is wearing that color is ber on each receipt so customers can voluntarily
chosen. Identify this sample as biased or unbi- call and participate.
ased and describe its type.

unbiased, stratified random biased, both voluntary and
Answer Answer
sample. convenience

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