The Seven Quality Control Tools

Description

Stratification is one of the original seven quality control tools. It is often used in combination with other tools. When data from many sources or categories has been mixed together, the analysis of the data can be difficult or even impossible. With the help of this technique tha data can be separated add some patterns can be seen [18].

When to Use

• Typical usage of stratification is when the data is acquired from several sources shifts, days of the week, population groups  and so on.
• When the acquired data must be separated to different sources or conditions

Procedure

1. As was mentioned in the description, the stratification is used in a combination with other tools. An example for a tool can be a scatter diagram, control chart, histogram, or other analysis tool. When the data is plotted a different marks or colors are used to distinguish data from various sources. Data which is separated this way is called stratified.
2. The subsets of stratified data must be analyzed separately.

Example

On the scatter plot (Fig. 1.15) the data is collected from three sources. A different sign and color is used for every source of data:

Fig. 1.15 A  scatter plot with data collected from three different sources