Week 3 tutorial for Experimental Design

Group 1 (Motor Trend Car Road Tests)

Members: MOHAMAD ZAHID BIN BAHAROM, ELOISE JINGYI YU, LIM HUI EN

# load the packages needed
library(ggplot2)
library(dplyr)

# Load the ‘mtcars’ data set 
{data(mtcars)}

Describe and summarize your assigned data set.

The mtcars dataset contains 32 observations and 11 variables.

Variable Description
mpg Miles per US gallon
cyl Number of cylinders
disp Displacement (cu. in.)
hp Gross horsepower
drat Rear axle ratio
wt Weight (1000 lbs)
qsec 1/4 mile time
vs Engine (0 = V-shaped, 1 = straight)
am Transmission (0 = automatic, 1 = manual)
gear Number of forward gears
carb Number of carburetors 
summary(mtcars)
##       mpg             cyl             disp             hp       
##  Min.   :10.40   Min.   :4.000   Min.   : 71.1   Min.   : 52.0  
##  1st Qu.:15.43   1st Qu.:4.000   1st Qu.:120.8   1st Qu.: 96.5  
##  Median :19.20   Median :6.000   Median :196.3   Median :123.0  
##  Mean   :20.09   Mean   :6.188   Mean   :230.7   Mean   :146.7  
##  3rd Qu.:22.80   3rd Qu.:8.000   3rd Qu.:326.0   3rd Qu.:180.0  
##  Max.   :33.90   Max.   :8.000   Max.   :472.0   Max.   :335.0  
##       drat             wt             qsec             vs        
##  Min.   :2.760   Min.   :1.513   Min.   :14.50   Min.   :0.0000  
##  1st Qu.:3.080   1st Qu.:2.581   1st Qu.:16.89   1st Qu.:0.0000  
##  Median :3.695   Median :3.325   Median :17.71   Median :0.0000  
##  Mean   :3.597   Mean   :3.217   Mean   :17.85   Mean   :0.4375  
##  3rd Qu.:3.920   3rd Qu.:3.610   3rd Qu.:18.90   3rd Qu.:1.0000  
##  Max.   :4.930   Max.   :5.424   Max.   :22.90   Max.   :1.0000  
##        am              gear            carb      
##  Min.   :0.0000   Min.   :3.000   Min.   :1.000  
##  1st Qu.:0.0000   1st Qu.:3.000   1st Qu.:2.000  
##  Median :0.0000   Median :4.000   Median :2.000  
##  Mean   :0.4062   Mean   :3.688   Mean   :2.812  
##  3rd Qu.:1.0000   3rd Qu.:4.000   3rd Qu.:4.000  
##  Max.   :1.0000   Max.   :5.000   Max.   :8.000

Graph your data and explore the relationship between car weight (wt) and miles per gallon (mpg)?

# Visualise the relationship between car weight (wt) and miles per gallon (mpg)
ggplot(mtcars, aes(x = wt, y = mpg) ) +     # what data for what axis
  geom_point(size = 3) +  #point size
  geom_smooth(method = "lm", se = TRUE, color = "red") +   # Adds a linear trend line for _colour_
  labs(  title = "Car Weight vs Miles per gallon",
         x = "Car Weight (1000lbs)",
         y = "Miles per gallon", ) +
  theme_minimal()    # Applies a clean theme to the plot.

There is a negative relationship between car weight and MPG, indicating that heavier cars generally have lower fuel efficiency.

Do cars with more cylinders (cyl) consume more fuel?

#copy paste boxplot code here

# use factor(__) for Cly, as one 3 cly values 4,6 and 8, treat as Categorical groups
# colour based on Cly value
# geom_violin() - trim = FALSE so do not cut of at min and max value
# overlay boxplot and points onto violin plot

# Create the violin plot with an overlaid boxplot
ggplot(mtcars, aes(x = factor(cyl), y = mpg, fill = factor(cyl))) +
  geom_violin(trim = FALSE, alpha = 0.3) +
  geom_boxplot(width = 0.15, fill = "white", color = "black") +
  geom_jitter(width = 0.05, alpha = 0.3, color = "black") +
  labs(
    title = "Cylinders vs Miles per Gallon",
    x = "Number of Cylinders",
    y = "Miles Per Gallon (MPG)",
    fill = "Cylinders"
  ) +
  theme_minimal()

#### Cars with more cylinders generally have lower MPG, indicating that they consume more fuel and are less fuel-efficient.