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Section #1 Quiz 1 Stem and Leaf Plot (N=29). X|8 2|2255667899999 3|0011222456668 4|00 Mean=29.9; M=30; Mode= 29; s=6.38;. Section #2 Quiz 1 Stem and Leaf Plot (N=36). X| 7 1|147889 2|244689 3|11122223333444567799 4|002 Mean=29.36; M=32; Mode= 32, 33; s=8.68;.

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Section 1 quiz 1 stem and leaf plot n 29
Section #1 Quiz 1 Stem and Leaf Plot (N=29)

  • X|8

  • 2|2255667899999

  • 3|0011222456668

  • 4|00

  • Mean=29.9; M=30; Mode= 29;

  • s=6.38;


Section 2 quiz 1 stem and leaf plot n 36
Section #2 Quiz 1 Stem and Leaf Plot (N=36)

  • X| 7

  • 1|147889

  • 2|244689

  • 3|11122223333444567799

  • 4|002

  • Mean=29.36; M=32; Mode= 32, 33; s=8.68;


Part ii s igma freud descriptive statistics

Part IISigma Freud & Descriptive Statistics

Chapter 5  

Ice Cream and Crime:

Computing Correlation Coefficients


What you will learn in chapter 5
What you will learn in Chapter 5

  • What correlations are and how they work

  • All about correlations...

    • How to compute them

    • How to interpret them

  • Other types of correlations that exist


What they are not
What they are not

  • Correlations only tell us about the relationship and the strength of the relationship.

  • Correlations do NOT tell us about cause and effect.


What they are not1
What they are not

  • Correlations do not imply causation

  • Examples

    • Marijuana use and heroin

    • Milk use and cancer

    • Church attendance and drug use

    • Lead levels and behavior

    • Cigarette smoking and Alzheimer’s

    • Education and sexual activity

    • Sex life and longevity

    • Coffee and suicide risk


What correlations are about
What Correlations are about…

  • Examines the relationship between variables

  • How the value of one variable changes in relation to changes in another variable

    • Range between -1 and 1

    • Bivariate correlation (2 variables)

    • Pearson product-moment correlation

      • Karl Pearson


Types of correlation coefficients
Types of Correlation Coefficients

  • Positive Correlation

    • Direction Correlation

      • When variables change in the same direction

  • Negative Correlation

    • Indirect Correlation

      • When variables change in opposite directions

        rXY = correlation between X and Y



Things to remember
Things to Remember

  • Correlations…

    • Range in value from -1 to +1

    • Absolute value indicates strength

    • Reflect situation where there are at least two data points

    • May want to use “indirect” and “direct” instead of “positive” and “negative” to keep from assigning value to the relationship


Computing simple correlations
Computing Simple Correlations

  • Pearson product-moment…

  • What do these symbols represent?


Steps in computation
Steps in Computation

  • List the two values for each participant

  • Compute the sum of X values, and compute the sum of Y values

  • Find square of sum for x and y

  • Find sum of squares for x and y

  • Find the sum of the XY products

  • Now “plug” these values into the formula


Pearson s product moment steps in the process
Pearson’s product-momentSteps in the process

  • Step 1:

    • Calculate

      • Σx

      • Σx2

      • (Σx)2

      • Σy

      • Σy2

      • (Σy)2


Pearson s product moment steps in the process1
Pearson’s product-momentSteps in the process

  • Step 2:

    • Calculate Σxy

    • Sometimes referred to as the sum of the cross-products

  • Step 3:

    • Substitute the values derived above into the formula

      • Note that N = number of pairs of scores







Is rate my professor valid
Is Rate My Professor Valid?

  • The Rate My Professor system relies on students who are willing to rate their professors anonymously. While this could encourage more candid feedback, the anonymous system has also at times provided what could be inaccurate ratings.


Is rate my professor valid1
Is Rate My Professor Valid?

  • One study showed the easier a class was and the more attractive the teacher, the more likely they would get a good rating on Rate My Professor. Others have expressed worry that Rate My Professor listings often give good ratings to teachers that may not provide the most comprehensive, educational, or quality courses available.



Computing simple correlations1
Computing Simple Correlations

  • Pearson product-moment…

  • What do these symbols represent?


Variance explained
Variance Explained

  • Coefficient of Determination

    • rxy = .70

    • .702 = .49 or 49%

  • Coefficient of Alienation

    • rxy = .70

    • .702 = .49

    • 1.00 - .49 = .51 or 51%


How variables share variance
How Variables Share Variance

  • Remember: Association NOT Causation



Using the computer
Using the Computer

  • Computing Correlation Coefficients using SPSS



Spss scatterplot
SPSS Scatterplot

  • Selecting Variables


Spss scatterplot1
SPSS Scatterplot

  • Entering variables


Spss scatterplot2
SPSS Scatterplot

  • Simple Scatterplot


Glossary terms to know
Glossary Terms to Know

  • Pearson-product moment correlation

  • Direct correlation

    • Positive correlation

  • Indirect correlation

    • Negative correlation

  • Scatterplot


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