STA 210 Lecture Notes - Lecture 2: Scatter Plot, Gonorrhea

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16 Feb 2017
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Part 1
Correlation and Causation
Correlation: tendency for certain values of one variable to be paired with certain other values of
another variable
Correlation in statistics has a more particular meaning
Example: Height and weight; taller people are usually heavier people
Scatterplot: A visual way of assessing association, both direction and strength
Most common way to describe the relationship between two variables
Positive association: points have an upward trend from left to right
Negative association: points have a downward trend from left to right
Strength: how tightly points are clustered about some clear pattern
Simple scatterplots are an informal, but useful visual means of addressing both the
direction and strength of the relationship between two variables that are appropriate for
this kind of plot
Part 2
Correlation Coefficient: a numerical way of summarizing that association between two
variables, provides those two can be represented in a scatterplot
The correlation coefficient measures the strength of the linear relationship between two
variables “x” and “y”
It is only appropriate to compute “r”if the scatterplot of y versus x exhibits a linear trend
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