Scatter Diagram | What is Scatter Diagram in 7 QC Tools? | Correlation Chart


Scatter Diagram | What is Scatter Diagram in 7 QC Tools? | Correlation Chart

What is a Scatter Diagram in 7 QC Tools:

Scatter Diagram is used to study and identify the possible relationship between two variables.
→ It is used to establish the existence of a correlation, Type of correlation, and Strength of the relation.
→ Scatter Diagram is the best validation tool of Basic Seven QC Tools.
→ It is a graph in which the values of two variables are plotted along two axes of the graph, the pattern of the resulting points will say the correlation between two variable.
→ It is also called a correlation chart.

➤ Examples of the relation between the two variables:

→ Weight and Height of a man.
→ Hardness and carbon content in the product.
→ Visual Inspection mistakes and Illumination levels.
→ Child’s height and Father’s height.
→ Curing Temperature and Curing Time
→ Advertising and sales


Four Easy Steps for Making a Scatter Diagram:

  1. Collect data for we have to find a correlation.
  2. Choose an independent and dependent variable.
  3. Construct the Graph and add the titles & trend line.
  4. Interpret the Graph


➤ Step 1. Collect data for we have to find a correlation between two variable:

→ Here we took 50 reading of curing temperature and curing time for a product 
→ We have to find is any correlation is present or not between curing temperature and curing time.
→ If we have more data sample then it will give a more precise result.

Data Collection Scatter Diagram in 7 QC Tools

➤ Step 2. Choose Independent and Dependent Variable:

→ The dependent variable is usually plotted along the vertical axis i.e. in Y-axis.
→ And dependent variable also called as a measured parameter.
→ The independent variable and is usually plotted along the horizontal axis i.e. in X-axis.
→ The independent variable also called as a control parameter.

➤ Step 3. Construct the Graph and add the titles & trend line:

Scatter Diagram in 7 QC Tools

➤ Step 4. Interpret the Scatter Diagram in 7 QC Tools:

→ While we are interpreting the Scatter Diagram then we will found seven different types of
     correlation between the two variable.


➤ The seven different correlation between variable

  1. Strong Positive correlation
  2. Moderate Positive correlation
  3. Weak Positive correlation
  4. Strong Negative correlation
  5. Moderate Negative correlation
  6. Weak Negative correlation
  7. Random Pattern (No correlation)
→ [1] Strong Positive correlation between two variable:
→ [2] Moderate Positive correlation between two variable:
→ [3] Weak Positive correlation between two variable:


Positive Co-relation in Scatter Diagram in 7 QC Tools

→ [4] Strong Negative correlation between two variable:
→ [5] Moderate Negative correlation between tow variable:
→ [6] Weak Negative correlation between tow variable:
→ [7] Random Pattern (No correlation) between two variable:

Negative Co-relation in Scatter Diagram in 7 QC Tools


Benefits of a Scatter Diagram:

→ It is beneficial to confirm a hypothesis (assumption) between two variables that these are related or not.
→ Provide both visual and statistical means to test the strength of a potential relationship.
→ It is a very good validation tool.
→ Used for proving the relation between cause and effect.
→ Plotting the diagram is relatively simple.


Limitation of the Scatter Diagram:

→ Scatter Diagram are unable to give you the exact extent of correlation.
→ It does not show you the quantitative measure of the relationship between the variable.
→ This chart does not show you the relationship for more than two variables at a time.