7-7 Selecting Samples
Preview
Warm Up
California Standards
Lesson Presentation
Holt CA Course 1
7-7 Selecting Samples
Warm Up
For each situation, explain whether it makes
sense to use a sample.
1. You want to know the most popular TV show
among teenagers in Los Angeles.
Yes; the population is large.
2. You want to know the favorite composer of the
music teachers at a small college.
No; the population is small.
3. The editor of a newspaper wants to know the
average age of the newspaper’s readers.
Yes; the population is large.
Holt CA Course 1
7-7 Selecting Samples
California
Standards
SDAP2.2 Identify different ways
of selecting a sample (e.g., convenience
sampling, responses to a survey, random
sampling) and which method makes a sample
more representative for a population.
Holt CA Course 1
7-7 Selecting Samples
Vocabulary
systematic sample
convenience sample
self-selected sample
Holt CA Course 1
7-7 Selecting Samples
Recall that in a random sample each member of
the population has an equal chance of being
selected. Some other types of sampling methods
are described below.
Sampling Methods
Method
Description
systematic sample
A member of the population is selected
at random, and then others are
selected by using a pattern.
convenience sample
The most-available members of the
population are chosen.
self-selected sample
Members of the population volunteer
to respond to a survey.
Holt CA Course 1
7-7 Selecting Samples
Random samples and systematic samples are
more likely to be representative of a population
than either convenience samples or self-selected
samples.
Holt CA Course 1
7-7 Selecting Samples
Additional Example 1: Identifying Sampling Methods
The manager of a company wants to know how many
employees have a laptop computer at home. Identify
each type of sampling method.
A. The manager randomly chooses 40 names from a list of all
employees.
This is a random sample because every employee has an equal
chance of being selected.
B. The manager surveys the first 50 employees as they
arrive at the office.
This is a convenience sample because the group of employees is
easy to reach.
C. The manager places a stack of survey forms in the
company cafeteria.
This is a self-selected sample because the group of employees
chooses whether to complete the surveys.
Holt CA Course 1
7-7 Selecting Samples
Additional Example 2: Analyzing Sampling Methods
Determine which sampling method will better represent
the entire population. Justify your answer.
Band Uniform Style
Sampling Method
Results
Maria surveys only the band
students she knows personally.
84% want blue uniforms
Jon writes each band student’s
61% want blue uniforms
name on a card. He questions those
students whose name he draws.
Jon’s sample is a random sample, giving every band
member an equal chance to be surveyed, so it is the
better method.
Holt CA Course 1
7-7 Selecting Samples
Check It Out! Example 1
You want to know how often students in high school
take tests. Identify each type of sampling method.
A. You survey the first 50 students as they arrive at school.
This is a convenience sample because the group of students is
easy to reach.
B. You place a stack of survey forms in the student library.
This is a self-selected sample because the group of students
chooses whether to complete the surveys.
C. You randomly choose 40 names from a list of all students
and then every 5th name after that.
This is a systematic sample because the students are chosen at
random and then the other names are chosen by using a pattern.
Holt CA Course 1
7-7 Selecting Samples
Check It Out! Example 2
Determine which sampling method will better
represent the entire population. Justify your
answer.
Swimming Scheduling
Sampling Method
Results
Ferdinand surveys every other
swimmer on the team.
72% want practice early
Anna-Maria questions the
swimmers who are in her Biology
class.
50% want practice early
Ferdinand’s method produces results that better
represent the entire swimming team population.
Holt CA Course 1
7-7 Selecting Samples
Lesson Quiz
An eye doctor wants to know how many of
her patients work at a computer. Identify
each type of sampling method.
1. The doctor surveys the patients in the waiting
room one morning.
convenience sample
2. The doctor places cards in the waiting room.
self-selected sample
3. The doctor chooses every 50th name from a
database of her patients. systematic sample
Holt CA Course 1