Histograms

When displaying grouped data, especially continuous data, a histogram is often the best way to do it – specifically in cases where not all the groups/classes are the same width.Histograms are like bar charts with 2 key differences:

• There are no gaps between the bars, and
• It’s the area (as opposed to the height) of each bar that tells you the frequency of that class.

In order to make this work, when drawing a histogram, we plot frequency density on the y-axis rather than frequency. The frequency density for each group is found using the formula:

Frequency Density = Frequency/Class width

To find the frequency from a histogram you find the area of the bar

Which would be class width x frequency density