Brook Luers
Teaching    >    Statistics 306, Fall 2017

Lab 3, September 26

Exercise 1


This exercise is inspired by a recent New York Times visualization of college enrollment rates by race/ethnicity. We will focus on public flagship universities.

Download enrollment.txt from our Canvas site and import the data set into an R data frame named enr.

(These data are from IPEDS, a survey conducted by the National Center for Education Statistics.)

Print the first few rows of enr in your R console. For each of the 50 public flagship universities, this data set contains the number (count) of new freshmen in each of five race/ethnicity categories (reth) for the years 1994–2015.

Assignment Part 1

Reference material: statistical transformations

First we will focus on the University of Michigan. Filter enr so it only contains data for Michigan:

umenr <- filter(enr, School=="University of Michigan-Ann Arbor")

Now recreate the following three plots. In parts (a) and (b), map the count variable to the y aesthetic and specify the appropriate position and stat arguments to geom_bar. In part (c), map the pct variable to the y aesthetic.

These graphs use a color palette developed by Color Brewer:

 +  scale_fill_brewer(palette='Set2',name='')

Which plot you think is more informative?

Assignment Part 2

Now recreate, as closely as possible, the NYT plot of all 50 public flagship universities, displaying the proportion of freshmen in each race/ethnicity category over time.

Use the pct variable in the enr data frame. You can remove the “other” category for simplicity.

Here is a code snippet to get you started. Fill in the ... with your own code.

ggplot(filter(enr, reth!="Other/unknown")) +
  ... # add the appropriate geom
  facet_wrap(...) + 
                     labels=...) + 
  ... + # change the axis labels 

My attempt is below. There are clearly some problems with the way I am calculating these percentages (e.g. University of Maine). Perhaps a future lab exercise will consist of properly downloading and computing these enrollment percentages.


Solutions to exercise 1