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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.

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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 relationship is very subjective. We will be determining a numerical summary called the correlation ( r) measures the direction and the strength of the linear relationship between two quantitative variables.

The formula for correlation of variables relationship is very subjective. We will be determining a numerical summary called the x and y for n individuals is:

TI relationship is very subjective. We will be determining a numerical summary called the 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 relationship is very subjective. We will be determining a numerical summary called the sparrowhawk colonies from section 3.1 A

Important facts to remember when interpreting correlation relationship is very subjective. We will be determining a numerical summary called the :1. Correlation makes no distinction between __________ and ________ variables.

explanatory

response

2. relationship is very subjective. We will be determining a numerical summary called the r does not change when wechange the unit of measurement of x or y or both.

3. Positive relationship is very subjective. We will be determining a numerical summary called the r indicates a ________ association between the variables and negative r indicates a ________ association.

positive

negative

4. The correlation relationship is very subjective. We will be determining a numerical summary called the r is always between ___ and ___. Values of r near 0 indicate a very _____ relationship.

weak

Example 1: Match the relationship is very subjective. We will be determining a numerical summary called the scatterplots below with their corresponding correlation r

2. Correlation does not describe 5 curvedrelationships between variables, no matter how strong.

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.