knitr::opts_chunk$set(eval = FALSE)

The weight and fuel efficiency of cars

Is there an association between the weight and the fuel efficiency of cars? To find out, we use the mtcars dataset from the datasets package. The mtcars data originally came from the 1974 Motor Trend US magazine, and it contains design and performance data on 32 models of automobile.

# ?mtcars # more info

Here, wt is weight in tons, and mpg is fuel efficiency in miles per gallon. We want to figure out if there is an association between wt and mpg. The mtcars dataset itself only has 32 rows, so we generated two larger bootstrapped datasets. We called them small and large.

head(readd(small)) # 48 rows
loadd(large)       # 64 rows

Then, we fit a couple regression models to the small and large to try to detect an association between wt and mpg. Here are the coefficients and p-values from one of the model fits.


Since the p-value on x2 is so small, there may be an association between weight and fuel efficiency after all.

A note on knitr reports in drake projects.

Because of the calls to readd() and loadd(), drake knows that small, large, and coef_regression2_small are dependencies of this R Markdown report. This dependency relationship is what causes the report to be processed at the very end.