Scatter Diagram in 7 QC Tools

Scatter diagram in 7QC Tools

Introduction

 - Scatter diagram is one of the tool in & QC tools and used to find the correlation between 2 variables.
 - It is also used to find the cause and effect relationship between two variables.
 - Scatter diagram is a graph in which two variables data are plotted against x-y axis and the pattern of plotted points shows the correlation.

When To Use Scatter Diagram

 - It is useful when you have two variables in which one is measureable and other is not.
 - When you have to find the cause and effect relationship between two variables.
 - When your dependent variable have multiple values for each figure of your independent variable.

Procedure To Draw Scatter Diagram

1. Collect the Data

 - Take one example that number of people who could balance on one foot for specific length of time.
 - In this example we have to find correlation is present or not.
Scatter diagram

2. Choose dependent and independent variable

 - The dependent variable  (Measurable) is plotted along the y-axis.
 - The independent variable (Control variable) is plotted along x-axis.
 - In this case no of people is an independent variable and time is dependent variable.

Scatter diagram

3. Construct the graph

- Now construct the graph based on all the data, add x-y axis name and make trend line.
Scatter diagram


4. Interpret the chart

 - Based on the trend line interpret the chart.

Types of Correlations


Based on the correlation and slope of the trend scatter diagrams are divided into 3 categories.

- Strong correlation- this type is also known as high degree of correlation. In this type plotted points are very close to each other and you can easily draw the trend line followed by pattern.
- Moderate correlation- this type also known as low degree correlation. In this type the plotted points are litter far and we can see that some kind of relation exists between 2 variables.
- No correlation- this type is also known as zero degree of correlation. In this type plotted points are spread randomly and we can't draw trend line through them.


By using this 3 correlations there are 3 types of scatter plots
 - Positive plot
 - Negative plot
 - Neutral plot

1. Strong correlation

Strong Correlation

2. Moderate correlation

Moderate Correlation

3. Weak Correlation

Weak Correlation

4. No relation

No Relation

Advantage of Scatter diagram

 - It shows correlation between 2 variables.
 - We can easily determined the range flow, i.e. maximum and minimum value.
 - Plotting the chart is easy.

Disadvantages of Scatter diagram

 - It is applicable for 2 variables only.
 - It cannot give you exact extent of correlation.
 - Number of observations are limited.

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