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.

11 variables (mpg) Miles/(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.