Warm Up

Read over the Activity at the beginning of Chapter 3 (p. 120)

AP Statistics, Section 3.1, Part 1 1

Section 3.1Part 1

AP Statistics

AP Statistics, Section 3.1, Part 1 3

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 4

Explanatory Variable

“An explanatory variable attempts to explain the observed outcomes.”

Independent variable

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Response Variable

A variable that measures an outcome of a study.

Dependent variable

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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?

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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 8

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 9

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 10

Figure 3.1 (Percent taking SAT vs. Score) Attributes of a good scatterplot

Consistent and uniform scaleLabel on both axisAccurate placement of dataData throughout the axisAxis break lines if not starting at zero.

To achieve this goal you are required to do your scatterplots on graph paper.

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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?

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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 14

Assignment

Exercises 3.1 – 3.11, (skip 3.5, 3.8) The Practice of Statistics.