Cube Nets

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A histogram is a visual representation of data using a set of vertical rectangles representing class frequencies. This is because it is a two-dimensional graph of frequency distribution that emphasises both the lengths and widths of the rectangles.

There are a few general rules for choosing bins:

1. Bins should be all the same size.
2. Bins should include all of the data, even outliers.
3. Boundaries for bins should land at whole numbers whenever possible (this makes the chart easier to read).
4. Choose between 5 and 20 bins.

The primary use of a Histogram Chart is to display the distribution (or “shape”) of the values in a data series. For example, we might know that normal human oral body temperature is approx 98.6 degrees Fahrenheit. To test this, we might sample 300 healthy persons and measure their oral temperature.

To draw a histogram for this information, first find the class width of each category. The area of the bar represents the frequency, so to find the height of the bar, divide frequency by the class width. This is called frequency density. Once the frequency densities of the numbers are known, the histogram can be drawn.

What is the class width? The class width is the difference between the upper or lower class limits of consecutive classes in a bin frequency table.

Creating a Grouped Frequency Distribution

1. Find the largest and smallest values.
2. Compute the Range = Maximum – Minimum.
3. Select the number of classes desired.
4. Find the class width by dividing the range by the number of classes and rounding up.
5. Pick a suitable starting point less than or equal to the minimum value.