Business Statistics

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Introduction:

This data set we have been assigned to analyze highlights the fuel-efficiency of the mentioned cars relative to several other variables.

One of the major issues most stressed upon to date is the ever-increasing threat of environmental degradation, global warming, and the need to conserve our scarce natural resources. This has led us to examine the fuel efficiency of cars. With rising gas prices, owning a car can become quite costly, not only eroding the owners disposable income, but also the Earth of its resources. It is not surprising that more and more consumers now desire to change their car, with fuel-efficiency being a major determinant. Since consuming less fuel is an important criterion, we believe that examining the relationship between different variables of cars and fuel-efficiency is a necessary study.

In order to get a true representation of the car population, we have used the data from a sample observing 20,001 cars of various classes, engine sizes, types, makes and models between the years 1978 to 2008. To fully incorporate the impact of weight on fuel efficiency (lurking variable) we also noted down the number of doors, passengers and luggage present in the car. The sample also includes the type of fuel used to see its effect on fuel efficiency.

Our goal will be to analyze the relationship between the transmission of the car, its size (class), the year of manufacture, the number of cylinders and engine displacement and fuel efficiency. Cars that can drive more miles per gallon of fuel used will be the most fuel-efficient. Inversely, cars that consume a lot of fuel will not be fuel-efficient.

Question 1-
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Transmission vs. Fuel Efficiency

In order to analyze the relationship between the transmission cars and fuel efficiency, we look at the following question:

What is the relationship between the transmission of the cars (i.e. Manual and Automatic transmission) to the City Miles/Gallon and Highway Miles/Gallon of Cars to determine which transmission type is more fuel-efficient.

According to our research, it is said that cars with manual transmission tend to consume less fuel, than automatic transmission cars. The loss in efficiency is due to automatic torque converters that require more energy than those of the manual cars. Secondly, Manual cars tend to weigh less, which means fewer cars for the gasoline engine to have to propel.

To prove this, we have compared the fuel efficiency of cars with manual and automatic transmissions. Furthermore, we have identified and ignored the effect of the lurking variables (impact of speed and driving styles) in order to simplify our data. To make sure each cluster is identical with the exception of transmission mode, we include all types of automatic transmissions (e.g. auto(3), auto(4) etc.) and followed the same concept for manual transmissions (e.g. manual(m4), manual(m5) etc.)

To determine which type of transmission if more fuel efficient, we made box and whisker plot below.

1.1 Box Plot for Average Highway Miles/Gallon

We look at the fuel efficiency of both automatic and manual transmission cars on the Highway. Comparing the interquartile ranges from the table in appendix 1.1a, we see that 50% of the manual cars fall between the range 21-31.49 mpg and 50% of the automatic cars lie between 19-26.80. This indicates the clear efficiency of the manual cars as against the automatic cars. When we referred back to the data, we identified presence of various outliers of various car models. The maximum value as indicated in the summary table shows outliers. Outliers for Manual cars include: Ford motor company & LINCOLN-MERCURY; 1984, 68mpg for manual cars, Honda Civic; 67mpg, Nissan Sentra; 66mpg, Volkswagen Rabbit; 61mpg and Pontiac; 60mpg. Further investigation of the data proved outliers for automatic...
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