Best practices for graphs
“Figures should be accurate, clear, and concise. As with tables, the figure with its title and legend should be understandable without undue reference to the text.”1
1. Line graphs for over-time data
Line graphs are the appropriate way to show change over time in one or a few groups. Your x-axis (horizontal) should be time, and your y-axis should be the quantity by which you want to see change over time. You can use different lines for different groups.
2. Bar graphs for group comparisons.
The bar graph is the Swiss army knife of data visualization. It’s useful because it is so versatile. Bar graphs use size to compare different quantities. Your y-axis is your quantity and on your x-axis you put your group categories.
3. Save the pies for dessert
Pie graphs are a great way to visualize proportions - parts that make up a whole. And, with a few nice colors, they’re attractive. They’re also simple.
But they can be a pain to create - to get right visually. They also lose their utility when you have more than a few categories. For this reason, the AMA discourages the use of pie graphs:
If you do want to use a pie graph, my advice to you is to keep it simple; use it only to show a few categories.