Tool 190: Stratification

AKA

Multiple Line Graph

Classification

Analyzing/Trending (AT)

Tool description

The stratification method stratifies (separates) an existing set of data into sub-groups to determine what effect each subgroup of data has on an abnormal pattern or condition. Stratification helps in isolating and unmasking the real cause of a problem.

Typical application

• To isolate abnormalities among data sets.

• To break down and analyze abnormal distributions.

• To verify the effects of subgroups to identify casue(s).

• To identify root causes of total variation.

• To analyze data to discover improvement opportunities.

Problem-solving phase

→	Select and define problem or opportunity
→	Identify and analyze causes or potential change
	Develop and plan possible solutions or change
	Implement and evaluate solution or change
→	Measure and report solution or change results
	Recognize and reward team efforts

Typically used by

1	Research/statistics
	Creativity/innovation
5	Engineering
2	Project management
3	Manufacturing
6	Marketing/sales
	Administration/documentation
4	Servicing/support
7	Customer/quality metrics
	Change management

links to other tools

before

• Line Chart

• Frequency Distribution (FD)

• Data Collection Strategy

• Checksheet

• Observation

after

• Variance Analysis

• Problem Specification

• Potential Problem Analysis (PPA)

• Trend Analysis

• Stratum Chart

Notes and key points

• Encode and designate all subgroups plotted. Preferably add the "total group" graph for instant comparisons. Apply the 3:4 ratio graph construction rule.

Step-by-step procedure

• STEP 1 Collect and verify data to be plotted. See example Shipping Errors over 8 Weeks.

  	Wk1	2	3	4	5	6	7	8
  Company Total:	40	32	30	34	41	29	39	27
  Workshift A	28	20	21	19	33	18	22	18
  Workshift B	8	7	4	8	3	6	10	4
  Workshift C	4	5	5	7	5	5	7	5

• STEP 2 Construct a stratification chart. The height of the vertical axis should be 75 percent of the length (100 percent) of the horizontal axis (3:4 ratio rule).

• STEP 3 Plot the data using the error totals for 8 weeks of all 3 workshifts. Also plot the company totals.

• STEP 4 Encode plotted data, designate lines, and label axes. Date the stratification chart.

Example of tool application