1. Types of Graphs…
and when to use them!

2. Bar Graphs

3. Bar Graphs
Used to compare amounts in data that represent different categories (these are called discrete data sets)
Categorical data is plotted on X-axis, quantitative (number values) on the Y-axis
Often used incorrectly to graph data with continuous X variables

4. Line Graph

5. Line Graphs Used to show trends
Variable plotted on X-axis must be continuous
A common type is “time series” where X = time

6. Scatterplot

7. Scatterplot (a type of line graph)
Used to show relationships between variables
X variable must be continuous
If one variable is believed to cause or explain changes in the other, that variable is plotted on the X

8. Histogram

9. Histogram Used when discrete X is converted to categories (“bins”)
Y axis represents frequency of data within each “bin”

10. Pie Chart

11. Pie Chart Used for same kind of data as bar chart
Must have data that represents all or 100% of something
Each slice = data category
Slice size shows relative proportion of observations within each category

12. Summary: Types of Graph
Graph type
Use
Line graph
Connects dots with lines
Used for continuous X data
Show patterns or trends
If time = X, time-series graph
Scatterplot
Display relationship between variables
Line of Best Fit or Trend Line
Bar graph
Used to show patterns
Should only be used when X data are categorical or discrete

13. Graph type
Description
Histogram
Similar to bar graph, but used when continuous X data are converted to categories
Pie chart
Compares small number of categories.
Works best if values are very different.
If similar, should label pie segments with actual values