section #1 quiz 1 stem and leaf plot (n=29) x|8 2|2255667899999 3|0011222456668 4|00 mean=29.9;...
TRANSCRIPT
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;
Part IIigma Freud & Descriptive Statistics
Chapter 5 Ice Cream and Crime: Computing Correlation Coefficients
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
Chapter 6 5
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.
Chapter 6 6
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…
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
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
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
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
Chapter 6 13
Pearson’s product-momentSteps in the process
Step 1: Calculate
Σx Σx2
(Σx)2
Σy Σy2
(Σy)2
Chapter 6 14
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
Correlation Matrix
Income Education Attitude Vote
Income 1.00 0.574 -0.08 -0.291
Education 1.00 -0.149 -0.199
Attitude 1.00 -0.169
Vote 1.00
Is Rate My Professor Valid?
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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.
Chapter 6 22
Now You Try!!
Participant Hours/Week Video Games College GPA
1 3 3.8
2 15 2.1
3 22 2.5
4 30 0.6
5 11 3.1
6 25 1.9
7 6 3.9
8 12 3.8
9 17 1.7
Variance Explained
Coefficient of Determination rxy = .70 .702 = .49 or 49%
Coefficient of Alienation rxy = .70 .702 = .49 1.00 - .49 = .51 or 51%