A slopegraph is a lot like a line graph, in that it plots change between points. However a slopegraph plots the change between only two points, without any kind of regard for the points in between. It is based on the idea that humans are fairly good at interpreting changes in direction. Decreases and quickly rising increases are easily detected.
Slopegraphs are often used to show change over time but have also been used to compare two groups, such as boys and girls.
Beginning of school year performance compared to end of year
In this example, the slope graph compares school performance at the beginning of the year (BOY) to the end of the year (EOY).
Source: Stephanie Evergreen
Advice for CHOOSING this option (tips and traps)
Choose this option when you want the audience to focus strictly on the beginning and end points. If, for example, a traditional line graph would reveal significant variations in the data, a slopegraph would not be the best choice because it masks any data points in the middle.
Advice for USING this option (tips and traps)
Though it might seem redundant, it’s helpful to label both points with the full category name and value. Otherwise, it can be tricky to follow the line, especially if the lines cross. Color coding lines of interest and matching the label color can also help draw out a story in a dataset.
Slopegraph theory and practice: Edward Tufte is responsible for introducing slopegraphs as a graph type.
Slopegraph template: Cole Nussbaumer shows a simple slopegraph and includes a downloadable template for her example so users can insert their own data easily.
Edward Tufte's slopegraphs in Excel: More complex slopegraphs are better displayed when the user can rollover lines to highlight its related information. At this link, the developers have created a mouseover technique for slopegraphs in Excel and included a downloadable template at the bottom.
Other ways to visualise changes over time
Displaying information as a series of data points connected by straight line segments, on two axes.
Split Axis Bar graph
Regraphing comparison between two points in time by simply graphing the change that has occurred in that time frame.
Visualising how a group of quantities changes over time. Items are "stacked" in this type of graph allowing the user to add up the underlying data points.