s519: evaluation of information systems
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S519: Evaluation of Information Systems. Social Statistics Inferential Statistics Chapter 14: linear regression. This week. How to predict and how it can be used in the social and behavioral sciences How to judge the accuracy of predictions INTERCEPT and SLOPE functions Multiple regression. - PowerPoint PPT PresentationTRANSCRIPT
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S519: Evaluation of Information Systems
Social Statistics
Inferential Statistics
Chapter 14: linear regression
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This week
How to predict and how it can be used in the social and behavioral sciences
How to judge the accuracy of predictions INTERCEPT and SLOPE functions Multiple regression
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Prediction
Based on the correlation, you can predict the value of one variable from the value of another.
Based on the previously collected data, calculate the correlation between these two variable, use that correlation and the value of X to predict Y
The higher the absolute value of the correlation coefficient, the more accurate the prediction is of one variable from the other based on that correlation
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Logic of prediction
Prediction is an activity that computes future outcomes from present ones.
When we want to predict one variable from another, we need to first compute the correlation between the two variables
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Type of regression
Linear regression One independent variable Multi-independent variables
Non-linear regression Power Exponential Quadric Cubic etc.
baxy bxaxaxay nn ...2211
cbxaxy 2
baxy xay
dcxbxaxy 23
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Example
high school GPA First-year college GPA3.5 3.32.5 2.2
4 3.53.8 2.72.8 3.51.9 23.2 3.13.7 3.42.7 1.93.3 3.7
Regression line, line of best fit
Y’ = bX + a
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Regression line
Y’ = bX + a
nXX
nYXXYb
/)(
)/(22
n
XbYa
Y’ = 0.704X + 0.719
Y’ (read Y prime) is the predicted value of Y
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Excel
Y’ = bX + a b = SLOPE() a = INTERCEPT()
high school GPA First-year college GPA3.5 3.32.5 2.2
4 3.53.8 2.72.8 3.51.9 23.2 3.13.7 3.42.7 1.93.3 3.7
Slope (b) 0.703893443intercept (a) 0.71977459
actual value predicted value3.25 3.007428279
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How good is our predication
Error of estimate Standard error of estimate
The difference between the predicated Y’ and real Y
Standard error of estimate is very similar to the standard deviation.
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Example
You are a talent scout looking for new boxers to train. For a group of 6 pro boxers, you record their reach (inches) and the percentage of wins (wins/total*100) over his career. Create a regression equation to predict the success of a boxer given his reach
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Example
Boxer Reach(X)
Win-p(Y)
A 68 40
B 80 85
C 76 64
D 82 94
E 65 30
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Example
Making predictions from our equation What winning percentage would you predict for “T-
rex Arms” Timmy, who has a reach of 62-inches
We would predict 18.44% of Timmy’s fights to be wins
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Example
Making predictions from our equation What winning percentage would you predict for
“Ape-Arms” Al, who has a reach of 84-inches?
We would predict 98.08% of Al’s fights to be wins
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Standard Error of Estimate