# Interpreting Scatterplots - PowerPoint PPT Presentation

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Interpreting Scatterplots. Presentation 2.3. Scatterplots. When looking at scatterplots, we will look for: Association (or direction) Form Strength Outliers. Direction. A trend that runs from the upper left to the lower right is said to have a negative association or direction.

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Interpreting Scatterplots

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## Interpreting Scatterplots

Presentation 2.3

### Scatterplots

• When looking at scatterplots, we will look for:

• Association (or direction)

• Form

• Strength

• Outliers

### Direction

A trend that runs from the upper left to the lower right is said to have a negative association or direction.

A trend running the from the lower left to upper right has a positive association or direction.

It is a lot like slope!

### Direction

• It is possible for a scatterplot to have no association or direction.

• This occurs when the plot looks like a random splattering of dots.

### Form

• Form:

• If there is a straight line (linear) relationship, it will appear as a cloud or swarm of points stretched out in a generally consistent, straight form.

• If the relationship isn’t straight, but curves, while still increasing or decreasing steadily, we can often find ways to make it more nearly straight.

### Strength

• Strength:

• At one extreme, the points appear to follow a single stream (whether straight, curved, or bending all over the place).

• At the other extreme, the points appear as a vague cloud with no discernable trend or pattern.

• Note: we will quantify the strength soon (that’s the r).

### Outliers

• Outliers:

• As before, points that do not follow the pattern.

• Outliers may be in either the x-direction, y-direction, or both directions.

• There’s no better example than the 2000 presidential election.

### Outliers

• 2000 Presidential Election

• Remember Florida

• The scatterplot on the next page details the number of votes for Bush and the number of votes for Buchanon.

• As you would expect, the more people voting for Bush should mean more people voting for Buchanon (since there are simply more people voting).

• In Palm Beach County there was much confusion about the ballot.

• The Democratic Party alleged that the ballot was poorly designed thus skewing the vote.

• The scatterplot shows the evidence.

### 2000 Presidential Election

• Apparently in Palm Beach County only, a disproportionate number of people voted for Buchanon.

• This point is a great example of an outlier.

• The outlier is in the y-direction (vertical).

• Why did this happen?

• The next slide shows the ballot voters used.

### Scatterplots

• Remember, when looking at scatterplots, look for:

• Association (or direction)

• Form

• Strength

• Outliers

### Scatterplots

• This concludes this presentation.