Stratification Analysis determines the extent of the problem for relevant factors.
Is the problem the same for all shifts?
Do all machines, spindles, fixtures have the same problem?
Do customers in various age groups or parts of the country have similar problems?
The important stratification factors will vary with each problem, but most problems will have several factors. Check sheets can be used to collect data. Essentially this analysis seeks to develop a pareto diagram for the important factors. The hope is that the extent of the problem will not be the same across all factors. The differences can then lead to identifying root cause.
When the 5W2H and Stratification Analysis are performed, it is important to consider a number of indicators. For example, a customer problem identified by warranty claims may also be reflected by various in-plant indicators. Sometimes, customer surveys may be able to define the problem more clearly. In some cases analysis of the problem can be expedited by correlating different problem indicators to identify the problem clearly.