Peer Assessment 1

#Loading the Data

library(datasets)
data <- mtcars
head(data)

##                    mpg cyl disp  hp drat    wt  qsec vs am gear carb
## Mazda RX4         21.0   6  160 110 3.90 2.620 16.46  0  1    4    4
## Mazda RX4 Wag     21.0   6  160 110 3.90 2.875 17.02  0  1    4    4
## Datsun 710        22.8   4  108  93 3.85 2.320 18.61  1  1    4    1
## Hornet 4 Drive    21.4   6  258 110 3.08 3.215 19.44  1  0    3    1
## Hornet Sportabout 18.7   8  360 175 3.15 3.440 17.02  0  0    3    2
## Valiant           18.1   6  225 105 2.76 3.460 20.22  1  0    3    1

Is an automatic or manual transmission better for MPG?

boxplot(data$mpg ~ data$am)

fit <- lm(mpg ~ am, data = mtcars)
stepFit <- step(fit, direction = "both")

## Start:  AIC=103.67
## mpg ~ am
## 
##        Df Sum of Sq    RSS    AIC
## <none>               720.9 103.67
## - am    1    405.15 1126.0 115.94

stepFit

## 
## Call:
## lm(formula = mpg ~ am, data = mtcars)
## 
## Coefficients:
## (Intercept)           am  
##      17.147        7.245

plot(fit)

The MPG difference between automatic and manual transmissions