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# AP Statistics Section 3.1B Correlation PowerPoint PPT Presentation

AP Statistics Section 3.1B Correlation. A scatterplot displays the direction , form and the strength of the relationship between two quantitative variables. Linear relations are particularly important because a straight line is a simple pattern that is quite common.

AP Statistics Section 3.1B Correlation

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### AP Statistics Section 3.1BCorrelation

A scatterplot displays the direction, form and the strengthof the relationship between two quantitative variables. Linear relations are particularly important because a straight line is a simple pattern that is quite common.

### We say a linear relation is strong if and weak if

the points lie close to a straight line

they are widely scattered about the line.

Relying on our eyes to try to judge the strength of a linear relationship is very subjective. We will be determining a numerical summary called the __________.

correlation

### The formula for correlation of variables x and y for n individuals is:

TI 83/84: Put data into 2 lists, say

STAT CALC 8:LinReg(a+bx) ENTER

Note: If r does not appear,2nd0 (Catalog)

Scroll down to “Diagnostic On”

Press ENTER twice

### Find r for the data on sparrowhawk colonies from section 3.1 A

Important facts to remember when interpreting correlation:1. Correlation makes no distinction between __________ and ________ variables.

explanatory

response

positive

negative

weak

6 4 2 1 3 5

### What effect does adding an outlier have on r and why?

4. Correlation is not a complete summary of two-variable data. Ideally , give the mean and standard deviations of both x and y along with the correlation.