Manual versus automatic transmission - a Shiny app to generate histograms of miles per gallon with adjustable bin size
author: Mark A. Jack date: 10/24/2015 font-family: 'Calibri'
A Shiny application is presented that allows to adjust the bin size in histograms illustrating the miles-per-gallon (mpg) for automatic and manual transmission from the data set mtcars.
The Shiny app - a 'bin size' slider
Figure 1: Two histograms of mpg values in mtcars data set for automatic (am=1) and manual transmission (am=0).
The bin size in both histograms may be adjusted interactively with a slide bar. The bin size can be varied between 1 and 40 in units of 1 mile-per-gallon.
See the web link below: https://mjgrav2001.shinyapps.io/mtcars-app
'mtcars' analysis results - linear regression
Figure 2:
- Two linear regression models for manual (am=0) and automatic (am=1) transmision.
- Left: Two fits with different slopes with mpg as outcome versus wt as predictor and interaction factor(am) wt.
- Right: Two fits with equal slopes when fitting mpg versus hp.
'mtcars' analysis results - residuals
Figure 3:
Distribution of normalized residuals of regression models (t-student distributions).
The Shiny app and its application results
The Shiny app allows to interactively adjust the bin size in mpg in a histogram. The bin size can be varied between 1 and 40 in units of 1 mile-per-gallon (mpg).
Main results:
- An average downwards shift of about 5 mpg can be seen when switching from am=1 to am=0.
- This differentiation is due to a relevant interaction factor(am) wt.
- Automatic transmission (am=1) favorable for higher gas mileage when weights are smaller.
- Cross-over happens around 3000 lbs where manual transmission (am=0) starts yielding higher mpg values.