Types of Graphs… and when to use them!

Bar Graphs

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

Line Graph

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

Scatterplot

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

Histogram

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

Pie Chart

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

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

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