1. AP Statistics September 30th, 2014 Mr. Calise
Section 3.1 Scatterplots
AP Statistics
September 30th, 2014
Mr. Calise

2. AP Statistics, Section 3.1, Part 1
Two Variables
Most statistical studies look at multiple variables.
Often the studies try to show a relationship between one variable and another
When one variable effects another, one variable will be referred to the explanatory variable and the other as the response variable
AP Statistics, Section 3.1, Part 1

3. AP Statistics, Section 3.1, Part 1
Explanatory Variable
“An explanatory variable attempts to explain the observed outcomes.”
AP Statistics, Section 3.1, Part 1

4. AP Statistics, Section 3.1, Part 1
Response Variable
A variable that measures an outcome of a study.
AP Statistics, Section 3.1, Part 1

5. AP Statistics, Section 3.1, Part 1
Example
A study looks at smoking and lung cancer.
Which (if any) is the explanatory variable?
Which (if any) is the response variable?
Is smoking a quantitative or categorical variable?
Is lung cancer a quantitative or categorical variable?
AP Statistics, Section 3.1, Part 1

6. AP Statistics, Section 3.1, Part 1
Example
A study looks at cavities and milk drinking.
Which (if any) is the explanatory variable?
Which (if any) is the response variable?
Is cavities a quantitative or categorical variable?
Is milk drinking a quantitative or categorical variable?
AP Statistics, Section 3.1, Part 1

7. AP Statistics, Section 3.1, Part 1
Example
A study looks at rain fall and SAT scores.
Which (if any) is the explanatory variable?
Which (if any) is the response variable?
Is rainfall a quantitative or categorical variable?
Is SAT scores a quantitative or categorical variable?
AP Statistics, Section 3.1, Part 1

8. AP Statistics, Section 3.1, Part 1
Scatterplots
A good way to try to see if there is a relationship between two quantitative variables is through the use of scatterplot.
On a scatterplot, we usually put what we think might be the explanatory variable on the x-axis and the response variable on the y-axis.
AP Statistics, Section 3.1, Part 1

9. Figure 3.1 (Percent taking SAT vs. Score)
Attributes of a good scatterplot
Consistent and uniform scale
Label on both axis
Accurate placement of data
Data throughout the axis
Axis break lines if not starting at zero.
To achieve this goal you are required to do your scatterplots on graph paper.
AP Statistics, Section 3.1, Part 1

10. AP Statistics, Section 3.1, Part 1

11. Interpreting Scatterplots
Pattern: linear, parabola, bell shaped
Deviations from pattern: Are there areas where the data conform less to the pattern?
Form: Are there clusters of data?
AP Statistics, Section 3.1, Part 1

12. Interpreting Scatterplots
Strength: Does the data tightly conform or loosely conform
Direction: If linear, is the data positively associated or negatively associated?
AP Statistics, Section 3.1, Part 1

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Using the TI-83
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21. AP Statistics, Section 3.1, Part 1
Assignment
Exercises 3.1 – 3.14, The Practice of Statistics.
AP Statistics, Section 3.1, Part 1