Analyzing Data and Determining Causes

Gathering data is only part of the puzzle in working towards lean Six Sigma status. When processes are found to be ineffective or a company's performance is found to be sub-standard, determining the root cause is critical in developing a program of corrective processes.

There are many tools available to clarify this part of the lean Six Sigma process. Each simplifies the process of digesting the data and identifying the source or sources of trouble within an organization's operation.

Fishbone Diagrams

The Fishbone Diagram is also known as a Cause & Effect or 'Ishikawa' Diagram, in honor of its creator, Dr. Kaoru Ishikawa of the University of Tokyo. No matter how it is named, this diagramming system identifies all likely contributing causes responsible for a particular problem.

Widely applicable to a number of circumstances, Fishbone Diagramming is extremely useful to process improvement teams. It provides the benefits of :

  • Allows for straightforward use and interpretation.
  • Educates and involves members of the workforce in resolving issues during its construction.
  • Targets the path of discussion to remained focused on the issues at hand.
  • Allows for thinking in terms of systems.
  • Prioritizes additional analysis and solutions.

The process of generating a Fishbone Diagram involves positioning possible causes tangentially from the central issue. Each cause is then further refined by using the 5-Why technique to uncover underlying, or root issues. The completed diagram uncovers a full picture of contributing factors and simplifies identification of over-riding problems. Such analysis plays an important role in successfully designing an effective lean Six Sigma process solution.

Histogram

This graphing technique distributes data in such a way that the spread and frequency of data is more readily apparent. When dealing with large pools of data that are otherwise cumbersome to analyze, histograms present the information in a more understandable format. Histograms are typically used to describe the relationship between a process output and customer expectations, issues critical in a lean Six Sigma organization.

5-Why Analysis

The 5-Why Analysis technique is particularly useful in uncovering the true cause of a problem. It promotes looking past surface factors to uncover exactly what is happening.

This process is based on the belief that by starting with the problem and asking 'Why?' five consecutive times, the true cause will be revealed. It is particularly common that by the final 'Why?', a management practice will be revealed as the source.

5-Why methodology is complimentary to Fishbone Diagramming as both break down issues to their most elemental level.

Regression and Correlation Analysis

Regression and Correlation Analysis examines the strength of correlation between variables in a Fishbone Diagram. This involves a statistical measurement called the Correlation Coefficient or ( r ).

The Coefficient can range between -1 and +1. A positive correlation is indicated by a value of +1 and the complete lack of correlation is indicated by -1.

When performing this analysis, it is significant to remember that correlation differs from causation. Because variables may be related, another variable may actually be responsible for the first two. Correlation Analysis shows relationships, rather than establishing causation.