Engineers New to being Expert Witness -- Scientific Method

DISCLAIMER: I am not a lawyer and anything written here is strictly my opinion and should not be taken as legal advice.

Once upon a time, the Courts in the U.S. would accept testimony from anyone who claimed to be an expert. So, courts would listen to the carefully worked out horoscope from an astrologist as well as the results of a exacting chemical experiment. There was no real distinction made.

Then came Frye v. United States in 1923, Court of Appeals in the District of Columbia. Here was a case where the use of blood pressure as a means of lie detection was submitted as evidence. The judge threw the evidence obtained this way out of the court as it was not an accepted criteria amongst the experts in the field. This case created the test for expert testimony: is it generally accepted in the scientific community for which it applies. This eliminated the lunatic fringe from testifying in court. Hurrah! Some rigor must be used in collecting evidence, evaluating and testing it. The principles the conclusions are drawn on must be generally recognized as valid in the field.

Thus it has become important to courts to get their evidence based on the Scientific Method. There are various forms to the Scientific Method depending on who you ask or how it is defined, but basically it is
a. Recognizing a problem or question exists.
b. Collecting information, data, and observations about it.
c. Analyzing the information
d. Make a hypothesis which explains known data and observations
e. Test the hypothesis. (If it fails then go back to 'b' with your results)
f. Make a final hypothesis which explains all known or observed phenomena
and test results.

When you are preparing for a case, that is the touchstone they will be using to determine your qualifications and your findings--can you cast your information in to a form which shows you followed this method, are your data acquired through scientifically rigorous means and are your conclusions based on accepted rinciples.

There are other criteria involved in being an expert witness, of course, but this is one of the key points to be aware of in preparing.

I will be writing more on other case law and the application to being an expert witness.

Finding Proximate Causes are only relative

I noticed today that I had been using the term "proximate cause" in reports for some time and wanted to track down the term a bit. Turns out to have quite a history for expert witnesses all the way back to old English law. Francis Bacon took the time to define it--I won't copy that definition here as his definition was somewhat Shakespearean in use of words.

However, here's the thing. The proximate cause is more or less a legal term used by expert witnesses and lawyers meaning that event which lead, ultimately, to the damage. This is a bit misty though. A fire investigator, as an expert witness, would say the proximate cause was the electric furnace failing. This the event which caused the damage or loss. Fair enough.

Then he calls in an engineer, who will take a different level of viewpoint, which is 'what is the proximate cause for this electric furnace catching fire?' He will dissect and analyze and study and may find that the thermal cut out failed. As an expert witness he may say "Ahah! The failure of the thermal cut-out was the event that lead to the loss." Fair enough.

The insurance company will want to subrogate and ask the furnace manufacturer to cough up some portion of the loss. The furnance manufacturer will naturally want to know why the heck the thermal cut out failed. They may acquire the very component or track back to manufacturing dates and component date codes and find that it was not the only one of that date code that had problems. They will then pursue the component manufacturer, say Fujitsu, and subrogate again.

Fujitsu will be unhappy with all this, of course, and have their own expert witness, forensic engineer, or manufacturing engineer do an analysis on why that component had a problem and they may find that there were chemical impurities in the device.

The chemical impurities were due to some failure on the part of, say, Dupont or Dow Chemical. Again proximate cause is being chased at increasing levels of detail.

Obviously, expert witnesses and forensic engineers tend to want to discuss the mechanical causality--the causal chain--the action and mechanical reaction of a series of concatenated events. One may easily find that the chemical impurities were due to an operator failure: end of the mechanical causal chain. But why did the operator fail? Then you are into the mental and emotional possibilities. His wife was leaving him, his child was found using drugs, etc, which so distracted him that he overlooked or flubbed his duties. (There are psychiatrists posing as 'expert witnesses' who could be consulted--but that's a hole we won't dive into.)

The point? Proximate Cause is NOT an absolute (which are unobtainable). It is only
a relative term for the sphere of operation we are talking about. The house should not have burned down, but it did because the furnace as a component of the house
failed. The furnace should not have started a fire, but it did because of the thermal cutout failure as a component of the furnace. The thermal cutout should not have failed... and so on.

Most expert witnesses understand this intuitively, but I realized it was a missing
element in any definition I could find. I also find that I will chase the causal chain as far as I can, beyond my sphere of operation, whenever possible, but can leave it to stand at the sphere of operation I am working in--for me as an expert witness/forensic engineer: one detail level below the fire scene investigator.

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