Finding the Root Cause



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Finding the Root Cause

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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.

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