Chapter 27

Question 1

Straight Enough Condition

Answer 1

for linearity. (Check that the scatterplot of y against x has linear form and that the scatterplot of residuals against predicted values has no obvious patterns.) ;)

Question 2

Independence Condition

Answer 2

Think about the nature of the data. Check a residuals plot.) ;)

Question 3

Does the Plot Thicken Condition

Answer 3

for constant variance. (Check that the scatterplot shows consistent spread across the range of the x-variable, and that the residuals plot has constant variance too, a common problem is increasing spread with increasing predicted values- the plot thickens.) ;)

Question 4

Nearly Normal Condition

Answer 4

for Normality of the residuals. (Check a histogram of the residuals.) ;)

Question 5

Residual standard deviation

Answer 5

The spread for the data around the regression line is measured with the residual standard deviation, se ;)

Question 6

t-test for the regression slope

Answer 6

When the assumptions are satisfied, we can perform a test for the slope coefficient. We usually test the null hypothesis that the true value of the slope is zero against the alternative that it is not. ;)

Question 7

Confidence interval for the regression slope

Answer 7

When the assumptions are satisfied, we can find a confidence interval for the slope parameter from b1 +-t*-2 X SE(b1). ;)