A histogram is a graphical representation of quantitative data. It has a continuous number line on the horizontal axis that is grouped into ranges, or class intervals. The quantity for each range is displayed as different column heights.
- Identify your variables.
Check the horizontal and vertical axes for any labels that identify what your variables are. These are required in order to understand what is being graphed and make conclusions from the subsequent data.
- Determine your class interval.
The class interval is the measure in units between two adjacent tick marks on the horizontal axis. In some cases, the class interval is 1.
- Find the corresponding quantity for the first range.
For the first range, or class interval, follow the bar up to the height of the column. Follow the height of the column over to the corresponding tick mark on the vertical axis. Reading the number beside the tick mark gives you the corresponding numerical quantity for the first group on the horizontal axis. In some cases, the quantity is zero, which is depicted by the lack of a bar or column, but the space remains in the class interval.
- Find the corresponding quantities for the remaining ranges.
Repeat the process of finding the column height for all remaining ranges or groups on the horizontal axis.