When you hear the word "evidence," what comes to mind? Many people think of crime scene investigations filled with forensics, mystery, and the hunt for a suspect. In a root cause analysis (RCA) investigation, the focus isn’t on who caused the incident, but we still need evidence to understand what happened and why.
In some investigations, the process of gathering and interpreting evidence is straightforward. In others, you don’t even know what you need until you start analyzing cause-and-effect relationships. In this blog, I’ll share my tips for gathering and managing evidence using the Cause Mapping® template.
Navigating the Variety of Evidence Types
Managing evidence in an RCA isn’t just about gathering information. It’s about knowing what to look for, securing it before it’s lost, and interpreting it effectively.
Personnel statements should be collected as soon as possible. Identify and speak with everyone who was in the proximity of the event and make note of their locations. Visiting the field and chatting with people in a comfortable setting often yields more useful details than a formal interview. I recommend asking a variety of both generic and specific questions to draw out more details. Generic questions help people think broadly, while specific questions can clarify key facts. If I take notes, I always read them back to ensure I didn’t misconstrue something
Broken parts, pieces, and components often disappear into dumpsters or leave the site on the back of contractor trucks. It's crucial to capture information about them right away and track their location. I've worked on investigations where parts were preserved, but without key details about where they were stored or who handled them, it took considerable effort to retrace their steps and resolve the issue.
Photos might seem like one of the easiest types of evidence to work with, but getting useful photos isn’t as simple as it seems. Close-up shots can lack context, while wide-angle images may obscure key details. I recommend taking pictures from a variety of distances and including objects such as a pen or your hand for scale. I always take at least three shots:
- A wide angle for context
- A medium zoom shot to figure out what we’re looking at from the wide angle
- A zoomed-in shot of the specific evidence
.png?width=1920&height=800&name=Pictures%20of%20Evidence-2%20(1).png)
Timeliness is also critical when it comes to photographic evidence. For example, I remember an incident where a piece of heavy machinery backed into an SUV. Witness statements described a congested area with dumpsters, but photos taken a few days later showed the area wide open, with no dumpsters in sight. The delay in taking the photos meant key details were missed. I always recommend taking a photo taken of the “as found” condition before anything is touched.
Diagrams bring clarity to an RCA, but they must be accurate. One person’s idea of a "barrier" might be caution tape, while another envisions a concrete wall. If you are creating your own diagrams, go to the actual site to capture details if possible. If you can’t do that, ask clarifying questions to understand the specifics regarding body positions, equipment locations, and so on.
Historical data must be interpreted carefully. Data collection rates vary, and timestamps across different systems may not align. For example, one case I encountered involved someone insisting that a rupture disc had burst prematurely because the pressure in the system never showed anything close to the set point. However, the system only collected data every 60 seconds, and during that interval, the pressure spiked and then dropped below the set point, which explained the discrepancy. If the sequence of events doesn’t add up, check the time on each system and be prepared to adjust for any offsets.
Policies, procedures, manuals, permits, and other documentation can be tricky to track down after an incident. It's crucial to gather the actual documents that were used during the incident, not just the official versions available online. In one investigation I facilitated, field workers were using outdated batch sheets they had pulled from the trash because they didn’t want to waste them. In another case, someone relied on a document saved on their desktop that was several versions behind.
The condition of these documents can also provide valuable clues. For instance, I once received a “field copy” that was straight-off-the-printer pristine, even though it was supposed to have been exposed to the elements for days.
Measurements should be sanity-checked. People often under- or over-estimate quantities, especially when it comes to spills. To test your own assumptions, try guessing how much area one gallon of water will cover. Then, go outside and see how far a gallon of water spreads on your driveway. You might be surprised!
Another simple test: Run a faucet with a pencil-sized stream of water for one minute and check how much water you collect. It’s a good way to calibrate your intuition and get a better sense of real-world measurements.
How to Manage Evidence with the Cause Mapping Template
While the best time to collect evidence is immediately, you don’t need to wait until all evidence is in hand before starting your analysis. Even in cases where I spent a lot of time gathering information before starting the analysis, I’ve never completed a Cause Map™ diagram without having to gather additional information in the process.
Begin mapping what you know and use the “Info to Get” box to track missing information.
Example 5-Why with Info to Get
Each “Info to Get” box is an action item to gather evidence. The Cause Mapping template includes a worksheet to track these action items, and it also provides designated places to document different types of evidence. Keeping all the evidence embedded in—or at least linked to—the Cause Mapping file creates a single source of truth, simplifying communication and long-term accessibility.
Once evidence confirms a possible cause, remove any question marks from the cause box and add an evidence box with a brief description.
Example 5-Why with Confirmed Cause and Evidence Box
If evidence disproves a cause, don’t delete it—cross it out and document why it was ruled out. This helps prevent redundant discussions and ensures future stakeholders understand why certain conclusions were reached.
Example 5-Why with Disproven Cause and Evidence Box
If I think someone will have a question on a possible cause—such as something that was stated early on, or a theory that a stakeholder keeps bringing up—I will intentionally add it, cross it out, and provide the disconfirming evidence. For example, in one case, a stakeholder insisted that a contractor was inexperienced. However, records showed the individual had 35 years of experience and had installed thousands of similar fittings. By adding an evidence box and crossing out inexperience as a factor, we eliminated this line of inquiry early.
Evidence and Analysis Go Hand in Hand
Effectively managing evidence strengthens an investigation and leads to more reliable findings. Prioritize key evidence early, stay organized with the Cause Mapping template, and don’t wait for perfect information before beginning analysis. The goal isn’t to collect everything—it’s to collect the right things and use them to construct a clear understanding of the incident. If in doubt, take the photo, save the part, and write it down. You can always discard unnecessary evidence, but recovering lost information later is much harder.
Evidence collection and cause-and-effect analysis are iterative. New evidence may confirm or challenge previous conclusions, refining your understanding as you go. By continuously integrating evidence into your Cause Map diagram, you create a dynamic, accurate picture of what happened and why—leading to stronger conclusions and more effective solutions.
