Populations and Samples

Chosing Appropriate Graphs to Represent Data

Frequency Table

• A way to organize data into categories or groups according to intervals

Cumulative Frequency

• Column in a frequency table that keeps a running total or the frequencies in each category.

Stem-and-leaf Plot

• Plot shows how ften data values occur and hot they are distributed• Leaf- on the plot represents the right hand digit• Stem- represents the left hand digits

Line Plot

• Shows data on a number line with an x or other marks to show the frequency of the data.

• Also known as Dot Plot

Bar Graph

• Compares the occurrences of data

Histogram

• Displays the frequency of data in intervals

Pie Chart

• Displays data in a circle to reveal the relationships of the parts to the whole

Line Graph

• Shows the relationship between two variables

Population

• The entire group of objects or individuals considered for the survey

Sample

• Part of the population

Convenience Sample

• Sampling the most available subjects in the population to obtain a quick result

Biased

• A sample that does not fairly represent the population

Random Sample

• A sample in which each member of the population has an equal chance of being selected

Practice

Determine which sampling method will better represent the entire population. Justify your answer.

Lone Star Cars: Customer Satisfaction

Sampling Method Results of Survey

Nadia surveys 200 customers on the car lot one Saturday morning

92% are satisfied

Daria mails surveys to 100 randomly-selected customers

68% are satisfied

Practice

Determine which sampling method will better represent the entire population. Justify your answer.

Melville Morning News: Subscription Renewals

Sampling Method Results of Survey

Sierra surveys 80 subscribers in her neighborhood

61% intend to renew their subscription

Samuel telephones 150 randomly selected subscribers

82% intend to renew their subscription

Essential Questions

• How do I chose and create appropriate graphs to represent data?

• What conclusions can be drawn from data?

TODAY…

• Graphs, tables, and plots can be used in about any situation depending on what the researcher wants; however, we will look at the most common uses.

• Use the graphic organizer given to you to categorize graphs, tables, and plots according to common usage. Keep this with you as we continue the presentation on populations so you may determine the best display to use for each scenario.

Scenario One

Damon wants to start a tutoring business somewhere in Nashville. He wants to find out family incomes in relation to the number of children. He sends a survey out to every 10th person in the phone book.

1. What is the population?

2. The sample is made up of ____?

3. Convenience sample or Random sample?

4. Is this sample biased?

5. Will the findings tell the true story?

6. Which type of display would best represent the data?

Relationship between variables

Line Graph

Histogram

Scenario Two

Roy wants to save money but doesn’t know what he spends it on each month. He collects all his bills and lists all his typical spending habits to find the percentage of each category.

1. What is the population?

2. The sample is made up of ____?

3. Convenience sample or Random sample?

4. Is this sample biased?

5. Will the findings tell the true story?

6. Which type of display would best represent the data?

Comparing differences within apopulation or between populations

Pie Chart

Histogram

Scenario Three

The mayor of New York would like to know if the people of the city would like to save money by eliminating holiday lighting on the streets. He categorizes them according to 15 districts as he knows 7 of the districts will determine he re-election. He sends a survey out to every 20th household listed on the tax registry.

1. What is the population?

2. The sample is made up of ____?

3. Convenience sample or Random sample?

4. Is this sample biased?

5. Will the findings tell the true story?

6. Which type of display would best represent the data?

Comparing difference between populations

Line graph

Bar graph

Scenario Four

The park manager of Macon wants to know how many people of different ages use the park. He takes a survey of all the people at the park for seven days.

1. What is the population?

2. The sample is made up of ____?

3. Convenience sample or Random sample?

4. Is this sample biased?

5. Will the findings tell the true story?

6. Which type of display would best represent the data?

Looking for occurrences

Line graph

Stem-and-leaf plot

Scenario Five

Coach Finch wants to see how many goals each soccer team in the district makes during the first game of the season. Out of ten teams in the league, she calls three of her friend coaches and asks. She then displays her findings.

1. What is the population?

2. The sample is made up of ____?

3. Convenience sample or Random sample?

4. Is this sample biased?

5. Will the findings tell the true story?

6. Which type of display would best represent the data?

Looking for occurrences

Line/dot plot

Stem-and-leaf plot

Complete the diagram and be prepared to share with the class.

http://nces.ed.gov/nceskids/createagraph/default.aspx?ID=70a1a23b6bde4023944373932de4f698

Discovery Education

Misleading Statistics