Project

Study of Fuel Efficiency for Imported and Domestic Passenger Cars

When people go to shop for a new car one of the main criteria they look at is the fuel

efficiency of the car. Many people who use fuel efficiency to determine what car to purchase

lean toward foreign made cars claiming that they get more miles per gallon than American

made cars. This study attempts to use the data for the average miles per gallon for domestic

and imported vehicles over a 24 year period from 1990-2013 to determine whether fuel

efficiency should play a significant role in whether to purchase a foreign made car over an

American made car.

The following table lists the average fuel efficiency of domestic and imported vehicles

from 1990-2013 based on data from the U.S. Department of Transportation found at

www.rita.gov

Table 1

Fuel Efficiency for Passenger Cars (mpg)

Year Domestic Imported

1990 26.9 29.9

1991 27.3 30.1

1992 27.0 29.2

1993 27.8 29.6

1994 27.5 29.7

1995 27.7 30.3

1996 28.1 29.6

1997 27.8 30.1

1998 28.6 29.2

1999 28.0 29.0

2000 28.7 28.3

2001 28.7 29.0

2002 29.1 28.8

2003 29.1 29.9

2004 29.9 28.7

2005 30.5 29.9

2006 30.3 29.7

2007 30.6 32.2

2008 31.2 31.8

2009 32.1 33.8

2010 33.1 35.2

2011 32.7 33.7

2012 34.4 36.4

2013 35.5 37.1

2 8

3 0

3 2

3 4

3 6

Boxplot for Imported MPG 2 8

3 0

3 2

3 4

Boxplot for Domestic MPG

Five Number Summary for the fuel efficiency of a Domestic passenger car with the

corresponding boxplot

Table 2

Five Number Summary for the fuel efficiency of an

Imported passenger car with the corresponding

boxplot

Table 3

Line graph comparing the fuel efficiency of a domestic vehicle to an imported vehicle from

1990-2013

Domestic mpg

Minimum 26.90

1st Quartile 27.80

Median 28.90

3rd Quartile 30.75

Max 35.50

Mean 29.69

Imported mpg

Minimum 28.30

1st Quartile 29.20

Median 29.90

3rd Quartile 31.90

Max 37.10

Mean 30.88

Bar graph comparing the fuel efficiency of a domestic vehicle to an imported vehicle from 1990-

2013

Domestic Imported

2 8

3 0

3 2

3 4

3 6

Side-by-side box plot

>

Determine whether the fuel efficiency varies enough that it should play a role in whether to

purchase an American or foreign made car.

H0 :μimported=μdomestic

Ha :μimported≠μdomestic

Using the two sample t-test we get the following test statistic

t0= x1−x2

√ s1 2

n1 + s2 2

n2

=1.678

and critical value t0.025=¿2.069.

A 95 percent confidence interval is given by (-0.2377, 2.62104).

Since the test statistic is smaller than the critical value we fail to reject the null hypothesis. Therefore fuel efficiency should not play a significant role in whether to purchase a foreign or an American made vehicle. References

United States, Bureau of Transportation Statistics, Department of Transportation. “Table 4-23: Fuel Efficiency of U.S. Light Duty Vehicles”. Retrieved August 4, 2015, from: http://www.rita.dot.gov/bts/sites/rita.dot.gov.bts/files/publications/ national_transportation_statistics/html/table_04_23.html