What is Histogram in 7 QC Tools

What is Histogram in 7 QC Tools?

→ “Histogram is a type of bar chart representing the frequency distribution of the data 
     from a process.”

1) What is Histogram?:

→“Histogram is a type of bar chart representing the frequency distribution of the data from a process.”
→ Only one parameter can be used for constructing the Histogram in 7 QC Tools.
→ The data should be variable data, i.e., measured on a continuous scale. ( eg. weight, time, temperature, dimensions, speed, etc.)



2) Key Concept of Histogram in 7 QC Tools:

    1. Data always have a variation
    2. Variation has Pattern
    3. Patterns can be seen easily when summarized pictorially

3) Steps for construction of Histogram in 7 QC Tools:

    1. Collect and record the data Points
    2. Compute the Range
    3. Determine the numbers of intervals
    4. Determine the interval width
    5. Summarize the data
    6. Construct the Graph
    7. Analyze the Histogram pattern


➤ Step 1. Collect and Record data:

→ For better analysis and forecasting of process collect at least 100 data points.
→ Here we take an example of 150 data points for making a Histogram in 7 QC Tools.


What is Histogram in 7 QC Tools

➤ Step 2. Compute the Range: 

 Largest Value        = 442
 Smallest Value      = 204
 Range of Values   =  442-204  = 238

➤ Step 3. Determine the No. of intervals required:

→ This step is for determining the no. of intervals required to construct Histogram in 7 QC Tools.


➤ Step 4. Determine the interval width:

→ Step 4 is for determining the width of intervals to construct Histogram in 7 QC Tools.

What is Histogram in 7 QC Tools

➤ Step 5. Summarize the data:

→ In Step 5 we will summarize the data as per the interval and count the frequency of data as per range value for construction of Histogram in 7 QC Tools.

➤ Step 6. Construct the Graph:

→ Now we will construct the Histogram by mentioning the Title, 
    Y-axis/Vertical axis = Interval width, X-axis/Horizontal axis = Interval width, 
    Graph - Trendline and Legend (if applicable).


What is Histogram in 7 QC Tools

➤ Must Mention below 5 parameters in Histogram:

     1. Title
     2. Y-axis/Vertical axis = Interval width
     3. X-axis/Horizontal axis = Interval width
     4. Graph - Trendline
     5. Legend (if applicable)
→ For a better understanding of these 5 parameters study below graph:


What is Histogram in 7 QC Tools

➤ Step 7. Analyze the Histogram pattern:

→ Interpretation of the Histogram
    ➧ Process Centering.
    ➧ Process Variation.
    ➧ Histogram Shape.
    ➧ Process Comparison with specification  (Process Capability).

4) Types of Histogram based on Pattern:

→ There are various types of Histogram pattern explain below :


    [A] Normal Distribution of Histogram:

          ➧ Bell Shaped Curve
          ➧ A peak in the middle


    [B] Skewed Distribution of Histogram:

          ➧ A peak is off center either right or left
          ➧ Analysis of very pure product is skewed i.e. product cannot be more than 100%.
          ➧ The range is not set properly for process


What is Histogram in 7 QC Tools

    [C] Double-Peaked / Bi-modal Histogram:

          ➧ Two Bell Shaped distributions.
          ➧ Maybe a combination of two processes or two shift’s data.



    [D] Multi Peaked / Multi-modal Histogram:

          ➧ Maybe data of several processes are plotted on the same graph.
          ➧ Range selection is not proper.


What is Histogram in 7 QC Tools

    [E] Edge Peaked Histogram:

          ➧ Borderline doubt for inspection and take it as ok.
          ➧ Instrument error.


    [F] Truncated or Heart-cut Histogram:

          ➧ The supplier might mix apart within spec and out of spec. limit.
          ➧ 100% of Incoming inspection and screening of mixed parts 


What is Histogram in 7 QC Tools

5) Benefits of Histogram in 7 QC Tools:

→ Summarize Large dataset Graphically
→ Confirms measurements to Specification
→ Excellent forecasting tool
→ Assist to decision making in the ongoing process

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See Also: Content 7 QC Tools
2. Flow Charts - 7 QC Tools
4. Check Sheet - 7 QC Tools
5. Histogram - 7 QC Tools
6. Pareto Chart - 7 QC Tools
7. Scatter Diagram - 7 QC Tools
8. Control Chart - 7 QC Tools