6.5.3 Biased Samples A is a portion of a population chosen

6.5.3 Biased Samples
A sample is a portion of a population chosen
to take part in a survey.
A biased sample is a sample chosen for a
survey, which may lead to incorrect
conclusions.
Biased samples can occur two ways:
1. If the sample selected is not representative
of the population to be surveyed.
Example:
The city council is going to
vote on whether to keep its
leash laws.
Sample 1 ~ survey dog
owners
Sample 2 ~ survey people who don’t have pets
Sample 3 ~ surveying some people who own
dogs and some who don’t.
Which sample shows the least bias?
Sample 3 ~ equal chances of yes or no answers
2. If the survey questions are worded in ways
meant to lead the people surveyed to give a
certain answer.
Example:
Wording 1 ~ Should the
mayor approve a bill
requiring dogs that are
outdoors to be on leashes at all times, instead
of running over people’s property?
Wording 2 ~ Should the mayor approve a bill
requiring dogs that are outdoors to be on
leashes at all times, instead of running freely
to exercise?
Wording 3 ~ Should the mayor approve a bill
requiring dogs that are outdoors to be on
leashes at all times?
Which wording shows the least bias?
Wording 3 ~ the other two wordings make it sound
like either a bad idea or good idea to let the dogs
run freely.
(6.5.3) Determine whether or not a sample is biased
Directions: Read the following survey scenarios and determine whether or not the sample is biased. Why or why not?
1. A town mayor wants to know if the residents of a town are in favor of building a new football stadium. On Saturday,
he randomly surveyed 50 male residents of the town to see if they were in favor of the new stadium.
2. A newspaper company wants to find out whether people prefer to get their newspapers delivered to their mailboxes
or to their front doors. To help get this information, the company will call 200 randomly selected people who get the
newspaper delivered and ask them to select their preferred delivery method.
3. Patrick asked the people waiting in line to buy tickets for a particular movie who their favorite actor was.
4. The patrons of a pet store were asked what their favorite type of pet is.
5. Steve wants to conduct a survey about fans’ favorite sports. In order to have a non-biased sample, he should
interview people leaving which facility?
a. football stadium
b. baseball park
c. mall
d. soccer field
6. The student body wants to survey the 8th grade class to choose a theme for the winter dance. They surveyed Mr.
Walker’s 3rd period art class.
7. Courtney wants to find out which class is most popular among the 7th and 8th grade students at her middle school.
She chose to randomly survey every ten students.
8. A movie theater surveyed patrons 45 years of age and older and asked what type of movie they prefer.
9. Louise surveyed all of her classmates in her 2nd period class; she asked whether they prefer watching football or
baseball.
10. Every twentieth student at Powell Middle School was asked what type of music he or she prefers
listening to.
11. Shoppers in the cat food section at a supermarket are asked about favorite dog foods.
12. Students are asked, “Are you willing to waste weekend time volunteering at an animal shelter?”
13. Parents are asked, “Should we develop hand-eye coordination in our children by teaching them how to
play computer games?”
6.5.3 Biased Samples Quiz
State whether or not a sample is biased. If so,
identify the source of the bias in the following
scenarios.
1. A movie theater surveyed patrons 45 years of
age and older and asked what type of movie they
prefer.
2. The student body wants to survey the 8th grade
class to choose a theme for the winter dance.
They surveyed Mr. Walker’s 3rd period art class.
3. The patrons of a pet store were asked what
their favorite type of pet is.
4. Students are asked, “Are you willing to waste
weekend time volunteering at an animal shelter?”
5. Parents are asked, “Should we develop hand-eye
coordination in our children by teaching them how
to play computer games?”