In: Statistics and Probability
A designer of a certain type of race cars asserts that painting a car increases its top speed by reducing drag. To test this, the top speeds (in mph) of six cars were measured on a track before and after painting. The results are shown in the table below. Test the claim that the mean of the differences (painted – not painted) for all race cars (paired T-test) is positive at the 95% confidence level. Do these results support the designer’s assertion?
| 
 Unpainted  | 
 214  | 
 208  | 
 198  | 
 216  | 
 208  | 
 213  | 
| 
 Painted  | 
 216  | 
 206  | 
 201  | 
 218  | 
 208  | 
 215  | 
Let us denote the difference
d = painted – not painted
There is not sufficient evidence to support
the designer’s assertion that the mean of the differences (painted
– not painted) for all race cars (paired T-test) is positive.