The Causal Chain -- mistakes in reasoning

Causal: "Of, involving, or constituting a cause" (please don't read it as "casual" which means "relaxed or informal")

I ran into a forensic engineer/expert witness from the West Coast who is famous (infamous) for his time consuming work. He proudly promotes himself as the most thorough forensic engineer around. He will spend days and days analyzing a stove which was the proximate cause for a fire. Something that most forensic engineers would take less than a day to complete.

What is missing is inteligence. Quantity mistaken for quality.

Any proximate cause is tied to a causal chain--a series of cause-and-effect leading from proximate cause to loss, damage or injury.

What is this 'expert witness' doing? He is examining everything whether it could be on the causal chain or not. Somewhat like investigating a boating accident by checking the salinity of the water. Yes, there was water. Yes, it has a salt content. Was it on the causal chain? Did the motor catch fire due to salt? Even if it did, why measure it? Simply finding that the motor specs included a caution never to be used near salt water and that it was in the Pacific Ocean would be sufficient. But no, it caught fire because of the leaking gas tank, punctured by a fishing gaff. Measuring the salinity of the ocean is superfluous.

A causal chain follows observable departures from ideal operation or condition which can be traced by an envisioned series of causes and effects. Expert witnesses in fire investigation are familiar with this: smoke damage in kitchen is a departure from the ideal condition of the walls, which should be free from much smoke damage. Fire investigator looks further and notes V-pattern near stove top. Looking closer finds a melted aluminum skillet with fried chicken debris at the bottom. All departures of ideal condition or operation. Bingo! And one can envision the sequence of events tracing back to the burned food in a melted pan.

Why measure paint thickness in the back bedroom? Is it related to the scene? Yes. Is it there to be measured? Yes. Is it part of the causal chain? Absolutely not. So why spend time measuring it once one has eliminated it? One has departed from an intelligent path of investigation by the expert witness.

Same with investigating a stove fire. Taking apart the stove and measuring each part and testing the full functionality of every screw, bolt, and resistor is very good for two things: running up a large bill and obscuring the case by a mountain of superfluous detail. Only thing worse would be intentionally presenting false data or conclusions.

This doesn't mean one shouldn't side check one's conclusions or explore other possible causal chains to be sure one has not misinterpretted the evidence. But spending too much time off the path is a waste of resources and money.

It is great for muddying the water though!


Derek Geer
Forensic Engineer/Expert Witness
San Diego, California
www.geers.com