ECO220Y1 Chapter Notes - Chapter 6: Scatter Plot, Square Root, Dependent And Independent Variables
ECO220
May 2018
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Ch. 6: Scatterplots, Association and Correlation
Scatterplot: a graph that shows the relationship between two quantitative variables measured on
the same cases
• If there is a lot of scatter, the relationship is weak and may not be useful for management
decision making
• Are the best way to start observing the relationship between two quantitative variables
Association
• Direction: a positive direction or association 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 association 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 association if there is little scatter around
the underlying relationship
Looking at Scatterplots
The first feature to look at is direction
• What's the sign - positive, negative or neither?
Direction:
• A pattern that runs from the upper left to the lower right is said to be negative
• A pattern that runs from the lower left to the upper right is said to be positive
The second thing to look at is form:
• Is it straight, curved, something exotic or no pattern?
o If there's a straight line relationship, it will appear as a cloud or swarm of points
stretched out in a generally consistent straight form
The third feature is the strength of the relationship
• How much does it scatter?
• Do the points appear tightly clustered in a single stream or do they seem to be so variable
and spread out that we can barely discern any trend or pattern
The final feature to look for are outliers: a point that does not fit the overall pattern seen in the
scatterplot
• Are there unusual observations or subgroups?
• Can lead us to probe further to understand our data more clearly
• Can be clue that you should split the data into subgroups instead of looking at them
altogether
LO 6.2 Assigning Roles to Variables in Scatterplots
Bivariate analysis: statistical analysis of two variables at the same time, as in our calculation of
the correlation coefficient and plotting of scatter diagrams
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ECO220Y1 Full Course Notes
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Document Summary
Scatterplot: a graph that shows the relationship between two quantitative variables measured on the same cases. If there is a lot of scatter, the relationship is weak and may not be useful for management decision making: are the best way to start observing the relationship between two quantitative variables. Association: direction: a positive direction or association means that in general as one variable increases so does the other. Direction: a pattern that runs from the upper left to the lower right is said to be negative, a pattern that runs from the lower left to the upper right is said to be positive. The second thing to look at is form: If there"s a straight line relationship, it will appear as a cloud or swarm of points stretched out in a generally consistent straight form. Lo 6. 2 assigning roles to variables in scatterplots.
