Collecting Data

Chapter 1 Lesson 6

Think about it…

Is there anything you would like to ask the rest of the eighth-graders at Indian Crest in a survey?

How would you go about surveying eighth-graders at Indian Crest? Would you survey every eighth grader? What are the pros and cons of surveying everyone? Would you only ask some of the students? How would you decide who to survey?

Key Terms

Sample: a small group used to represent a population.

Population: a large group of data

What makes a good sample?

1. Selected at random

2. Representative of the population

3. A large enough number to provide accurate data

Is this a good sample?

One hundred people in Lafayette, Colorado were asked to eat a bowl of oatmeal every day for a month to see whether eating a healthy breakfast daily could help reduce cholesterol. After 30 days, 98 of those in the sample had lower cholesterol. Is this a good sample?

GOOD SAMPLES?

Two hundred students at a school basketball game are surveyed to find the students’ favorite sport. – No, more students will say basketball.

Every other person leaving a supermarket is asked to name their favorite soap to determine the average shopper’s favorite soap. – Yes, it is random and representative.

Survey of Indian Crest Students

You want to know the average amount of time students at Indian Crest and Indian Valley spend on homework per night. – What would be a good sample to gather

data about this topic through a survey?– Give an example of a sample that would

not be a good way to gather this information through a survey.

Frequency Tables

After you complete a survey, the data you gather needs to be organized. One way to organize your data is in a frequency table.

In a frequency table, you use tally marks to record and display the frequency of events.

How to Make a Frequency Table

Make a table with three columns: Time, Tally and Frequency. Add a Title.

Average Temperatures for U.S. Cities

Temperatures Tally Frequency

Step 2: Determine your intervals and label them.

Average Temperatures for U.S. Cities

Temperatures Tally Frequency

35-39

40-44

45-49

50-54

55-59

Step 3: Use tally marks to record the

times in each interval.

Average Temperatures for U.S. Cities

Temperatures Tally Frequency

35-39 II

40-44 IIII I

45-49 IIII IIII

50-54 I

55-59 I

Step 4: Count the tally marks in each row and record this number in the frequency

column.

Average Temperatures for U.S. Cities

Temperatures Tally Frequency

35-39 II 2

40-44 IIII I 6

45-49 IIII IIII 10

50-54 I 1

55-59 I 1

Cumulative Frequency Tables

Frequency Table DataRecord High Temps. For U.S. States

Temp (ºc) Tally Frequency

35-39 II 2

40-44 IIII I 6

45-49 IIII IIII 10

50-54 I 1

55-59 I 1

Cumulative Frequency Table

Record High Temps. For U.S. States

Temp (ºc) Frequency Cumulative Frequency

35-39 2 2

40-44 6 8

45-49 10 18

50-54 1 19

55-59 1 20

Journal

Explain the difference between a frequency table and a cumulative frequency table.

List some examples of how a survey might be biased.