Scores from Exam 1:
41 59 10 71 0 45 57 49 78 64 62 12 89 71 52 68 84 65 90 69 31 55 63 20 64 52 80 51
45 95 32 97 76 54 41 82 60
What is the mean and standard deviation of the above sample?
If we assume performance is a bell-shape curve:
If A’s should have a z-score of at least 1.25 (top 10%), what score would be the cut-off for an A?
If B’s should have a z-score of at least .25 (top 30%), what score would be the cut-off for a B?
If C’s should have a z-score of at least -.25 (above bottom 30%), what would be the cut-off?
Location of the k percentile: L = k * n
(where if you’re looking for the top 10%, k = .1)
(note, we use this formula for the first and third quartile with k = .25 and .75)
Class Curve:
Top 10% (90th percentile) of class gets an A, what’s the position in the above the lowest A?
Top 30% (to 10%, the 70th percentile) gets a B, what’s the position in the above of the lowest
B?
Middle 40% gets a C (30th percentile to 70th percentile), what’s the position in the above of the
lowest C?
Year
Poverty% Unemp%
1980
1985
1990
1992
1995
1998
2000
2002
2005
2007
2009
13
14
13.5
14.8
13.8
12.7
11.3
12.1
12.6
12.5
14.3
Predicted

Y (Y )
Residual
7.6
7.4
5.2
7.8
5.6
4.5
4
5.8
5
4.6
9.5
Regress the Poverty Rate (Y) on the Unemployment Rate (X)
For each Unemployment Rate, calculate the predicted Poverty Rate (the 4th column)
Then find the residual (error, 5th column)
What is the r and r2, interpret both of these
Interpret b1
Interpret the Y intercept
Find the X intercept and interpret that
Predictions:
If the unemployment rate was to fall by 3% points, predict what happens to the poverty rate
If the unemployment rate rose to 11%, predict the poverty rate
Control (important assumption):
What the unemployment rate need to be in order to get the poverty rate to 10%?
Car
Weight
(pounds)
3175
3450
3225
3985
2440
2500
2290
Mileage
(mpg)
Predicted

Y (Y )
Residual
27
29
27
24
37
34
37
Regress the Mileage on the Car Weight
Calculate the Predicted Y and the Residual
What is the r and r2, interpret both of these
Interpret b1
Interpret the Y intercept
Find the X intercept and interpret that
Predictions:
If you add 500 pounds to a car, what happens to the mileage?
If a car weighs 2800 pounds, what is the predicted mileage?
Control (important assumption):
How heavy should a car be if you want the mileage to be 50 mpg?