Bimodal Histogram, Histogram with two peaks

What is a bimodal Histogram and how to interpret its results.

Bimodal Histogram, Histogram with two peaks

Bimodal HistogramBimodal

A bimodal shape, shown above, has two peaks. This shape may show that the data has come from two different systems. If this shape occurs, the two sources should be separated and analysed separately.


Bimodal Histogram

Can also be called a Multi-modal. This type of histogram has two or many peaks. The “mode” is the most frequently accruing number within a sample, in the bimodal or multi-modal distribution there are two or more clusters of higher frequency numbers arising. They result when the data comes from two or more distributions, for example if you are using two different machines in the one production line, two sources of the same raw material, different shifts etc.

In order to fully understand and interpret the bi-modal histogram, the sources of the two (or more) distributions needs to be identified and individual histograms should then be plotted.


A bimodal histogram can also arise, there the data for the histogram is taken over a period of time. In this situation, a change may have arisen within the process to cause the mean of the data to change, resulting in the two data peaks. In such a situation the process should be investigated over the period of time related to the data being collected to determine what could have changed within the process, for example, was the data collected over two shifts with different process operators. Could the environmental conditions have changed (a warm day versus a cold day), were different items of test equipment used to record measurements, etc. Hence its preferred to separately analyze both peaks.bimodal histogram, bimodal histogram, bimodal histogram

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