# Correlation. Median HHI and Percent of Households Eligible for Food Stamps.

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Correlation

Median HHI and Percent of Households Eligible for Food Stamps

Percent of Households Eligible for Food Stamps and Percent Unemployed

A few words about Scatterplots A Scatterplot displays the direction and strength of the association between two sets of quantitative data The direction refers to whether there is a positive, negative, or no association between the data The association is strong if the dots come close to being in a straight line The association is weak if the dots don’t come close to being in a straight line

A number called the correlation measures both the direction and strength of the linear relationship between two related sets of quantitative variables.

Properties of Correlation The correlation is written as r Correlation requires that both variables be quantitative A positive value for r means there is a positive relationship between the variables A negative value for r means there is a negative relationship between the variables

The value of the correlation is always between - 1 and + 1. A strong relationship means the correlation is close to either - 1 or + 1 There can be a strong positive relationship (r is close to 1), or a strong negative relationship (r is close to - 1) A weak relationship means the correlation is closer to 0 than to either - 1 or + 1 The value of r is affected by outliers

Guess the Correlations:.67.993.003 -.975

Excel Formula for Correlation: =CORREL(array1,array2) AB 132 248 3711 434 582 657 =CORREL(array1,array2) =CORREL(a1:a6,array2) =CORREL(a1:a6,b1:b6)

Percent of HH Eligible for Food Stamps New AIDS Cases per 100,000 (2000) Percent of 35 – 44 y/o with Bachelor ’ s Degree Percent Unemployed Percent Unemployed and Not in Labor Force Spending per Student (Grades 1 – 8) Median HHI (1999) -0.950-0.6590.873-0.895-0.6870.147 Percent of HH Eligible for Food Stamps 0.771-0.8750.9230.675-0.052 New AIDS Cases per 100,000 (2000) -0.7610.5850.2680.194 Percent of 35 – 44 y/o with Bachelor ’ s Degree -0.735-0.4290.043 Percent Unemployed 0.666-0.070 Spending per Student (Grds 1 – 8) -0.007

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