No formula for finding root causes exists.

• Start by studying symptoms.
• Group causes into like categories.

• Look for chains of causes.

• Are the causes interrelated?

Causal Influence Numbers (CINs) can help when dealing with complex problems. See an example CIN Worksheet.

• Determining a Causal Influence Number can help point the way when:
  • A problem is so complex with so many relationships between the causes that the root cause is not obvious.
  • A complex problem has several (root) causes contributing to the problem.
• Causal Influence Numbers rate the impact of cause on the effect on a relative rating scale of 1 to 100.
  • The higher the rating, the greater the impact and the more probable that the cause is the root cause.
  • See the Appendix for generic CIN Frequency Rating Influence Rating Scales.

To draw conclusions, data must be collected and analyzed.

• Visual displays of data often provide the most helpful clues.
• Standard data collection tools include:
  • Data collection forms
  • Checklists
  • Tally (or check) sheets
• The following are both data collection and data display tools.
  • Run Charts (Trend Charts)
  • Histograms
  • Scatter Diagrams
  • Concentration Diagrams
  • Workflow Diagrams
• Data display tools and techniques include:
  • Standard charts and graphs
  • Pareto Diagrams
  • Run Charts (Trend Charts)
  • Histograms
  • Scatter Diagrams
  • Concentration Diagrams
  • Workflow Diagrams
  • Cause and Effect Diagrams
• Data analysis tools and techniques include:
  • Control Charts (SPC)
  • Tests of Significance
  • Correlation and Regression Analysis
  • Multivariate Analysis
  • Time Series Analysis
  • Design of Experiments
  • Failure Analyses
  • Simulations

Investigative tools may be needed to "question the process."

• Investigative tools include:
  • The Five-Whys
  • Comparative Analysis (What Is-What Is Not)
  • Timeline Analysis
  • FMEA (Failure Mode and Effects Analysis)
  • Fault Tree Analysis
  • Design of Experiments
  • (See the Appendix for Worksheets for the Five-Whys and Comparative Analysis and for additional information on Timeline Analysis and DOEs.)

What if the root cause is still unknown?

• If the root cause is still hidden from view, it is time to retrace the steps taken, starting way back with the Problem Statement.
• Something may be "missing;" ask:
  • Is the task clear?
  • Has the process been properly defined?
  • Does the team have the necessary skills, knowledge and experience to tackle the job?

Parting thoughts regarding finding the root cause:

• Rarely will all tools and techniques be needed to uncover a root cause. Experience is the best judge to determine the best order to use the various tools and techniques available to search and question processes for the root cause to a specific problem.
• When the root cause is found, always ask the "root cause question:

"Does this cause (or causes) explain all that we know about what the problem is, as well as all we know about what the problem isn't?"

• If answer is a resounding "YES," the root cause has most likely been found and hearty congratulations are in order.