# 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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