Histograms vs Bar Charts

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.
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How to find the Frequency Density

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

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Finding Frequency

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

Which would be class width x frequency density

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