STAT 451, Day 4

Let's do this!

Video

What to Look For, Patterns

  • Looking for questions via exploring patterns can lead to more questions with possibly even more interesting answers.
  • Usually, if we see something we didn't expect to see, we can start with “Why is this phenomena there?”

Example

Consider the bike data which represents four years of quar- terly mountain bike sales. Fit a time series regression model using seasonal dummy variables. Estimate the next year of sales by quarter.

quarter=rep(1:4,4)
bike = ts(c(10,31,43,16,11,33,45,17,13,34,48,19,15,37,51,21), frequency=4,
start=c(2007,1))
plot.ts(bike)

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Better View

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What to Look For, Relationships

  • Oftentimes, this means finding and exploring relationships betweeen multiple variables.
loadstuff <-c("ggplot2", "devtools", "dplyr", "stringr", "maps", "mapdata")
lapply(loadstuff, require, character.only=TRUE)

ggplot(mtcars, aes(x=wt, y=mpg)) + geom_point(shape=18, color='blue', size=5)

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Better View

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Multiple Variables

# Change point shapes and colors
require(ggplot2)
ggplot(mtcars, aes(x=wt, y=mpg, shape=factor(cyl), color=factor(cyl))) +
  geom_point(size=5)

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Better View

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Design

  • Time spend on designing your graphic will be a waste if people don't know what it means.
  • Explain what it means with lables, legends, and keys.
  • Label your axes, with appropriate units if applicable
  • Include your sources
  • Consider your audience
  • 2-D versus 3-D

Example

What's wrong with this? Let's reproduce it.

Scale

Changing the aspect ratio and/or scale can distort your message.

Visual Cues

  • Position
  • Length (scale)
  • Angle
  • Direction
  • Shape
  • Area
  • Volume
  • Shade / Color

More Examples of Bad Visualizations

Baseline?

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Ummm…

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A key fact that wasn't on the chart: the cost of not going to college has diminished even more. Than means, your prospects as a high school graduate are a lot worse than your prospects as a college graduate.

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If you live with your Mom, Dad, brother Joe and cousin Sam, and Sam was (briefly) on some kind of welfare program, that counted against you and everyone in your household.

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A pictograph is basically a bar graph which is made up of a picture related to the topic of the graph. When the picture grows in two dimensions, width as well as height, it misleads the viewer by presenting a two-fold growth in the area or size of the picture