How the TapRooT® Root Cause Tree® Diagram Helps You Collect Evidence
Most investigators open their TapRooT® Root Cause Tree® Diagram for the first time during an investigation when they are ready to start their root cause analysis. They collect evidence, build a sequence of events, identify Causal Factors, and then begin analyzing why the incident occurred.
The TapRooT® Root Cause Tree® Diagram and Root Cause Tree® Dictionary are designed to guide root cause analysis. But they also serve another valuable purpose: helping investigators recognize what they still do not know.
The First Explanation Isn’t the Whole Story
After an incident, explanations often develop quickly:
- The employee did not follow the procedure.
- The equipment failed.
- The worker was not paying attention.
- Communication broke down.
- Someone made a wrong decision.
These statements may contain part of the truth but they are often conclusions based on incomplete information. “The procedure was not followed,” for example, describes an action. It does not explain the conditions surrounding that action.
Was the procedure available? Did it match the work being performed? Could the steps be completed as written? Had the equipment changed since the procedure was written? Had employees developed an informal workaround?
Until investigators can answer questions like these with evidence, they are not ready to to start the root cause analysis.
Evidence Collection Has More Than One Phase
The initial phase of evidence collection is broad. Investigators identify and preserve information from people, paper, physical items, and recordings. They visit the scene, take photographs, gather records, speak with the people involved, and begin organizing the information on a SnapCharT® Diagram.
The next phase is more focused.
Investigators review what they have collected and ask:
- What information is missing?
- Which statements have not been verified?
- Where are we relying on assumptions?
- What additional evidence would help us understand the suspected Causal Factors?
This is where root cause analysis tools can strengthen evidence collection.
Use the Tools to Find Gaps, Not Confirm Conclusions
A common mistake is opening the Root Cause Tree® Diagram and immediately looking for a root cause that fits the investigator’s hunch about what happened.
That approach can reinforce confirmation bias. Once investigators believe they know why something happened, they naturally notice evidence that supports the belief and may overlook information that challenges it.
A better approach is to use the Root Cause Tree® Diagram and Dictionary to generate questions. The tools encourage investigators to consider areas such as procedures, training, communication, work direction, equipment design, human engineering, quality control, and management systems.
The purpose is not to examine every possible category in depth. It is to identify areas where the existing evidence is incomplete.
If a question cannot be answered with documented facts, the investigation may need another interview, document review, site visit, equipment inspection, or tabletop review.
Let the Causal Factors Guide the Search
Suspected Causal Factors give investigators a logical place to collect evidence.
For each Causal Factor, look at the surrounding Events and Conditions on the SnapCharT® Diagram. Then use the Root Cause Tree® Diagram and Dictionary to consider what additional information might be necessary.
The questions may reveal that an apparently simple human performance issue involves conditions that were not documented during the initial site visit. An equipment problem may require maintenance records, inspection results, design information, or a history of similar failures.
As new evidence is collected, it should be added to the SnapCharT® Diagram.
This creates a stronger factual foundation for the analysis that follows.
Better Analysis Begins with Better Evidence
Used for evidence collection, the Root Cause Tree® Diagram and Dictionary can expose gaps in the investigation, improve follow-up questions, and reduce the likelihood that assumptions will be treated as facts. The goal is to enter root cause analysis with enough evidence to confidently support or rule out potential causes.
Before analyzing your next incident, ask:
What questions can’t we answer yet?
The unanswered questions may lead you to the evidence that changes the investigation.
Coming Early Next Year
This article is adapted from the upcoming second edition of Evidence Collection and Interviewing Techniques to Sharpen Investigation Skills. The book provides practical tools for collecting stronger evidence, planning effective site visits, and improving investigations by following the evidence wherever it leads.
Join us for the Effective Interviewing and Evidence Collection course at the 2027 Global TapRooT® Summit. You’ll receive a copy of the new book and a chance to put it into practical use.
