1. Warm Up
To qualify for security officers’ training, recruits are tested for stress tolerance. The scores are normally distributed, with a mean of 62 and a standard deviation of 8. If only the top 15% of recruits are selected, find the cutoff score.

2. Think/Pair/Share
Ideal boyfriend or girlfriend.

3. Dr. Ballard’s Little Problem
I am 5’2”. My husband is 6’7”. Is that weird?
Do women typically date/marry men taller than themselves?
Do tall women typically date taller men than do short women?
How could I find out?

4. Chapter 4 Overview
Chapter 3 dealt with descriptions of a single variable.
Chapter 4 presents basic data analysis for relationships between two quantitative variables.
The most common statistical tools discussed:
scatterplots
correlation
least-squares regression

5. Today’s Essential Question:
What is a scatterplot, how do I create one, and what does it tell me?
S.ID.6 Represent data on two quantitative variables on a scatter plot, and describe how the variables are related.

6. Lesson 6: Scatterplot
A scatter plot is a graph made by plotting ordered pairs in a coordinate plane to show the relationship between two sets of data.
Scatter plots will easily show a relationship exists between two sets of data .

7. Examples
The scatter plot shows the hours of study and test scores of 20 students.
As the number of hours of study increases, the marks scored tend to increase.

8. Taller or Shorter?
I wonder if tall women tend to date taller men than do short women. So I gathered data from teachers here at GMC! The data is on the handout.
Construct a scatterplot to show the relationship between women’s and men’s heights.

9. Taller or Shorter?

10. Response vs. Explanatory
In many studies more than one variable is recorded per case or individual. It is often the purpose of the study to determine if and/or how one or more variables affect another.
Response Variable—A variable you would be interested in predicting. A result. Often called a dependent variable. Plotted on the y-axis.
Explanatory Variable—Any variable that explains the response variable. A cause. Often called an independent variable. Plotted on the x-axis.
What was women in my example? Men? Why?

11. Examples
Determine which variable is the explanatory variable and which is the response variable. In cases with no relationship write none.
Hair length and shoe size
A family’s income and the years of education their child completes
Price of a house and square footage
Amount of time spent studying and grade on exam
The weight of a person and the height of a person
A student’s scores on the SAT Math test and the SAT Critical Reading test

12. How to Save a Life
Studies have shown that people who suffer sudden cardiac arrest have a better chance of survival if a defibrillator shock is administered very soon after cardiac arrest. How is the survival rate related to the time between when cardiac arrest occurs and when the defibrillator shock is delivered? The question is addressed in the paper “Improving Survival from Sudden Cardiac Arrest: The Role of Home Defibrillators.” The data below give the survival rate (percent) and mean call-to-shock time (minutes) for 5 different cardiac rehabilitation centers.
Construct a scatterplot to show the relationship between survival rate and mean call-to-shock time.
Call-to-shock time (min.) 2 6 7 9 12
Survival rate (%) 90 45 30 5

13. How to Save a Life

14. Want a Quicker Way? L1: Explanatory/independent/x
L2: Response/dependent/y
2ndStatPlotPlot1
On1st type
Xlist: L1
Ylist: L2
Zoom9:ZoomStat

15. Today’s Essential Question:
What is a scatterplot, how do I create one, and what does it tell me?

16. Interpreting Scatterplots
Look for an overall pattern.
Form:
Strength:
Direction:

17. Form Examples

18. Strength Examples

19. Positive
A scatter plot describes a positive association if, as (x variable) set of  values  increases, the other (y variable) values tends to increase. 

20. Negative
A scatter plot describes a negative association if, as (x variable) set of values increases, the (y variable) set tends to decrease.

21. None
A scatter plot shows no association if the ordered pairs show no trend.

22. Direction Examples

23. Examples, Revisited
Determine whether the data would show a positive, negative, or no correlation.
Hair length and shoe size
A family’s income and the years of education their child completes
Price of a house and square footage
Amount of time spent studying and grade on exam
The weight of a person and the height of a person
A student’s scores on the SAT Math test and the SAT Critical Reading test

24. Let’s Tie the Knot! Materials: rope, measuring tape, paper, pencil
What is the relationship between the length of a rope and the number of knots tied in it?

25. We’re Tying the Knot… Response variable: Explanatory variable:
Demonstration
Collect your data!
Plot your data—by hand, please 
Describe your data—direction, strength, form
Save your data—I’ll collect to use on Wednesday

26. Today’s Essential Question:
What is a scatterplot, how do I create one, and what does it tell me?

27. Scatterplot Worksheet Due Wednesday
Homework
Scatterplot Worksheet
Due Wednesday

28. 3-2-1 Ticket Out The Door
3 things you did today
2 things you learned
1 question you still have