Histogram | Different Types | Examples

What is a Histogram graph in 7 QC Tools?

→ It is a type of bar chart representing the frequency distribution of the data from a process.
→ Only one parameter can be used for constructing this chart.
→ It is a frequency distribution tool of the Basic 7 QC Tools for the process improvement.
→ The parameter must be variable data, i.e., measured on a continuous scale. ( eg. weight, time, temperature, dimensions, speed, etc.)
→ This tool is used in the DMAIC Methodology of Six Sigma Project

What is a histogram used for?

It is used for showing a large data set graphically
Problem forecasting
Study the variation in the ongoing process

Key Concept of Histogram in 7 QC Tools:

➨ The Key Concept is:
⇢ Data always have a variation
⇢ Variation has Pattern
⇢ Patterns can be seen easily when summarized pictorially

How to Make a Histogram?

→ Seven Steps are mentioned below for making the histograph:

Data Collection
Compute the Range
Determine the numbers of intervals
Determine the interval width
Summarize the record
Construct the Graph
Analyze the pattern of the chart

[01] Data Collection:

→ For better analysis and forecasting of process collect at least 100 record points.
→ Here we take an example of 150 record points for making a chart.

[02] Compute the Range:

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

[03] Determine the No. of intervals required:

→ This step is for determining the no. of intervals required.

[04] Determine the interval width:

→ Step 4 is for determining the width of intervals to construct.

[05] Summarize the record:

→ 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 the_graph.

[06] Construct the Graph:

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

➨ Five Important Parameters in Histogram:
⇢ Title
⇢ Y-axis/Vertical axis = Interval width
⇢ X-axis/Horizontal axis = Interval width
⇢ Graph - Trendline
⇢ Legend (if applicable)
⇢ For a better understanding of these 5 parameters study below chart:

[07] Analyze the Graph pattern:

→ Interpretation of the Graph
⇢ Central Tendency
⇢ Process Variation
⇢ Histogram Shape
⇢ Process Capability (Comparison with the specification)

Examples of Histogram Graphs

Types of Histogram Patterns

→ Various types of Histograms based on patterns are mentioned below
➨ [A] Normal Distribution:
⇢ Bell Shaped Curve
⇢ A peak in the middle

➨ [B] Skewed Distribution:
⇢ A peak is off-center either right or left
⇢ Analysis of very pure products is skewed i.e. product cannot be more than 100%.
⇢ The range is not set properly for operation

➨ [C] Double-Peaked / Bi-modal:
⇢ Two Bell Shaped distributions.
⇢ Maybe a combination of records of two processes or two shifts.

➨ [D] Multi Peaked / Multi-modal:
⇢ Maybe readings of several processes are plotted on the same graph.
⇢ Range selection is not proper.

➨ [E] Edge Peaked:
⇢ Borderline doubt for inspection and take it as ok.
⇢ Instrument error.

➨ [F] Truncated or Heart-cut:
⇢ The supplier might mix apart within spec and out of spec. limit.
⇢ 100% of Incoming inspection and screening of mixed parts.

Benefits of Histogram:

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

👉 Also Read:

1. Flow Chart | Process Flow Diagram | Types & Examples

2. Cause & Effect Diagram (Fishbone or Ishikawa)

3. Check Sheet | Different Types & Examples

4. 7 QC Tools for Process Improvement

5. Pareto Chart | Example & Principles

6. Scatter Diagram | Types & Examples

7. Control Chart | Types & Examples

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