Chapter 6

Scatterplots

Scatterplots

A ___________ shows the relationship between two quantitative variables measured on the same cases.

Timeplot

A ________ displays data that change over time. Often, successive values are connected with lines to show trends more clearly. Sometimes a smooth curve is added to the plot to help show long-term patterns and trends.

Association

• DIRECTION: A positive direction or ___________ means that, in general, as one variable increases, so does the other. When increases in one variable generally correspond to decreases in the other, the ___________ is negative.

• FORM: The form we care about most is straight, but you should certainly describe other patterns you see in scatterplots.

•STRENGTH: A scatterplot is said to show a strong ___________ if there is little scatter around the underlying relationship.

Outlier

A point that does not fit the overall pattern seen in the scatterplot.

y-axis
response variable
x-axis
explanatory variable

In a scatterplot, you must choose a role for each variable. Assign to the ______ the ________ ________ that you hope to predict or explain. Assign to the ______ the ___________ or predictor ________ that accounts for, explains, predicts, or is otherwise responsible for the __________

Correlation Coefficient

The ___________ ____________ is a numerical measure of the direction and strength of a linear association here:

Ladder of Powers

The ______ __ _______ places in order the effects that many re-expressions have on the data.

Re-expression

We __________ data by taking the logarithm, the square root, the reciprocal, or some other mathematical operation of all values of a variable.