""Get the facts first, and then you can distort themas much as you please."

Mark Twain

3.1 SCATTERPLOTS (Pages 106 -122)

OVERVIEW: Many statistical studies involve more thanone variable. A scatterplot represents a graphical display thatallows one to observe a possible relationship between twoquantitative variables.

 (Y) * * * r * * e * * * s * p * * o * n * s e (X ) explanatory variable

When we think that changes in a variable x explain, or evencause, changes in a second variable y, we call x anexplanatory variable and y a response variable. Important: Even if it appears that y can be"predicted" from x, it does not follow that x causes y.Association does not imply causation.

When examining a scatterplot, look for an overall pattern.These words and phrases relate to scatterplots.

• Direction
• Form
• Strength
• Positive association
• Negative association
• Outliers

Extremely important for success of the Advanced PlacementStatistics Examination:
If you are given a numerical data set, always (I repeat,always) display the shape of the distribution.
Using the TI-83, this can be done very easily with a histogram or aboxplot.

 These brilliant Algebra II students are using their textbooks to demonstrate the concept of association. What are they illustrating? (A) Positive association. (B) Negative association. (C) No association.