Supplemental Materials for Data Visualization

The purpose of this document is to provide additional options for visualiziation of data. Questions about code can be directed to Alicia Vallorani (auv27@psu.edu).

Scatterplots

When you have a large number of data points, you can add jitter to the points (i.e., slightly vary the location of the points) to handle this overplotting issue.

# Scatter plot with jitter
ggplot(sat.act, aes(age, ACT, color=education)) +
  geom_point(position="jitter") +
  ylab("Score") +
  xlab("Age") +
  labs(color="Education level") +
  ggtitle("ACT scores by age and education level") +
  theme_classic()

# Scatter plot with jitter short-cut
ggplot(sat.act, aes(age, ACT, color=education)) +
  geom_jitter() +
  ylab("Score") +
  xlab("Age") +
  labs(color="Education level") +
  ggtitle("ACT scores by age and education level") +
  theme_classic()

Bar Graphs

# Bar graph with additional element stacked
ggplot(sat.act, aes(education, ACT, fill=sex)) +
  geom_bar(stat="summary", fun.y="mean") +
  scale_fill_grey() +
  ylab("Average score") +
  xlab("Education level") +
  labs(fill="Sex") +
  ggtitle("Average ACT scores at each education level by sex") +
  scale_y_continuous(expand=c(0,0)) +
  theme_classic()

# Bar graph with additional element dodged
ggplot(sat.act, aes(education, ACT, fill=sex)) +
  geom_bar(stat="summary", fun.y="mean", position="dodge") +
  scale_fill_grey() +
  ylab("Average score") +
  xlab("Education level") +
  labs(fill="Sex") +
  ggtitle("Average ACT scores at each education level by sex") +
  scale_y_continuous(expand=c(0,0)) +
  theme_classic()

Instead of plotting the bars side-by-side, we can use facet_wrap() to create separate graphs for each sex. It’s also possible to set the limits on the axes manually, so the bars don’t run into the labels.

# Bar graph with additional element stacked
ggplot(sat.act, aes(education, ACT, fill=sex)) +
  geom_bar(stat="summary", fun.y="mean") +
  facet_wrap(~sex) +
  scale_fill_grey() +
  ylab("Average score") +
  xlab("Education level") +
  labs(fill="Sex") +
  ggtitle("Average ACT scores at each education level by sex") +
  scale_y_continuous(expand=c(0,0), limits=c(0,36)) +
  theme_classic()

Interactions

ggplot(sat.act, aes(x=as.factor(education), y=SATV, fill = sex)) +
  geom_boxplot() + 
  geom_jitter(position=position_jitterdodge(), alpha = .2) + 
  labs(fill = "Sex",
       x = "Education")

Visualizing Chi-Squared.

vcd::mosaic(~ sex+education, data = sat.act, shade = TRUE, legend = TRUE)