Histogram, or Frequency Histogram is a bar graph. The horizontal axis depicts the range and scale of observations involved and vertical axis shows the number of data points in various intervals ie. the frequency of observations in the intervals.
Histograms are popular among statisticians. Though they do not show the exact values of the data points they give a very good idea about the spread of the data and shape.
Let us try drawing a histogram of percentage scores in a test . The scores are as follows :-
82.5, 78.3, 76.2, 81.2, 72.3, 73.2, 76.3, 77.3, 78.2, 78.5, 75.6, 79.2, 78.3, 80.2, 76.4, 77.9, 75.8, 76.5, 77.3, 78.2
When any data is provided to XLMiner™, it decides the size and number of intervals amongst which the data should be distributed. It uses "Nicing" to decide the number of intervals. Five to Twenty intervals are fixed on the dataset depending on its range.
Now see the histogram of the same data.
The values on the horizontal axis are the upper limits of bins (intervals) of data points, and not the mid-points of the intervals, although they may appear to be so. This is in keeping with the way the Analysis Toolpak of Excel works. As an example, the bar shown against 78 has a frequency of 7. That means 7 data points lie in the range above 76 and upto (including) 78.
As is evident, the histogram gives a fairly good idea about the shape and spread of data at a glance.
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