Histogram: The way of data analysis and QC tool

As been a Quality Engineer or Industrial Engineer we must know the 7 QC tools. And one of the important QC tool is Histogram.

In this post you will learn more details about this tool. How and the way of data analysis using the important QC tool.

What is Histogram?

Histogram is the visual tool for presenting the variable data. And also it organize the data to describe the process performance.

Additionally it shows the amount and pattern of the variation from the process. The date you collected will be arrange in manner, it will show you the variation and spread of data.

Therefore it is the most powerful tool in 7 QC tools.

Why do we get variation?

Variation is essentially a law of nature. Therefore we can’t eliminate the variation.

Output quality characteristics depend upon the input parameters.

It is impossible to keep input parameters constant. There will be always variation in the input parameters. Since there is variation in the input parameters, there is also variation in the output characteristics

Learn more about why do we get variation?

Definition of Histogram

The pictorial nature of the histogram enables us to see patterns that are difficult to see in a table of numbers.


Key Concept of Histogram

  • Data always have variation
  • Variation have pattern
  • Patterns can be seen easily when summarized pictorially
Presentation of Distribution

Example with data

Data Table – Weight of Bars in kg.

Weight of Bars in kg.
Picturization of Data

Study of Histogram

So, now you draw the graph base on the data you have. But if you dont know how to study it then no use. Therefore here are some points which you should look into it and interpret the data. Refer below points:

  •   Location of mean of the process
  •   Spread of the process
  •   Shape of the process
Location of process in histogram
Location of the Process
Spread of histogram
Spread of the Process
Shape of histogram
Shape of the Process

Constructing Histogram

Basic Elements for Construction of Histogram

For constructing it we need to know the following:

  • Lowest value of the data set
  • Highest value of the data set
  • Approximate number of cells graph have
  • Cell width
  • Lower cell boundary of first cell
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