Problem of the Day
Use the scatter plot of year vs. number of flights to answer the following. (The correlation is .828.)
1. Describe the association. Are there unusual points? Comment on their meaning or significance.
2. Find and interpret r2.
Problem of the Day
If the point in the upper right corner of this scatterplot is removed from the data set, then what will happen to the slope of the line of best fit (b) and to the correlation (r) ?
A) both will increase.
B) both will decrease.
C) b will increase, and r will decrease.
D) b will decrease, and r will increase.
E) both will remain the same.
Problem of the Day
A philosophy professor has found a correlation of 0.80 between the number of hours students study for his exams and their exam performance. During the time he collected the data, students studied an average of 10 hours with a standard deviation of 2.5 hours, and scored an average of 80 points with a standard deviation of 7.5 points.
Create a linear model to estimate the number of points a student will score on the next exam from the number of hours the student studies.
If a student studies for 15 hours, what score should the student expect on the next exam?
Problem of the Day
Here is a scatterplot of weight versus height for students in an introductory statistics class. The men are coded as ‘1’ and appear as circles in the scatterplot; the women are coded as ‘2’ and appear as squares in the scatterplot. Describe the association.
Chapter 9 Regression Wisdom
­residuals will indicate whether linear regression is appropriate
­What if they indicate that it isn't?
Further analysis may be needed
­factors affecting what cereal you buy
­_____________ variables
­when final report is done, what info is actually relevant
Extrapolation
­when we have a linear model that is appropriate, it is still limited.(use x = 50 inches, 75 inches)
ShoeSize = ­12.31 + .31Height
Unusual Points
­Outliers
­Leverage
­Influential
Practice Problems
Make a scatterplot of the table
(which shows the number of graduating classes in a given year).
Create a model that best represents
the number of graduating classes
in a given year. How many models
would be appropriate?
(What classes should you use and why?)
Is it appropriate to use your models? Why or why not? When?
Use a model to predict the number of classes in 2010. Is there a problem with this projection?
Wandering Point Activity
Practice Problems
Use the scatterplot of the average number of strikeouts by a pitcher predicted by the average speed of their fastball throughout
a season.
Is there a pattern?
Any unusual points? What are
their significance?
Would a scatterplot of a single month of the season have a stronger association? Why or why not?
Practice Problems
Describe the association
between SAT participation
and SAT Scores.
If the left,top point (4,1215) were removed, would the correlation get stronger or weaker?
The graph below plots average crawling ages (in weeks) against the mean temperatures when the babies were 6 months old. The researchers found a correlation of r = ­0.70.
Explain (in context) what the slope of the line means.
Explain (in context) what the y­intercept of the line means.
In this context, what does a negative residual indicate?
Readings and Examples pgs 201 ­ 213
Homework: pgs 214­220:1­3,9,15,21,23,25,29
Exit slip(the following analysis predicts brain weight from body weight, I have no idea what the units are)
Use the following regression analysis for Brain Weight vs. Body Weight
Find the correlation.
Write the regression equation.
Interpret r2.
Interpret the y­intercept in context.