"If an investigator can never say that of the hypotheses considered one is believed to be correct based on the fact it could not be disproved using all the data available than what is the purpose of the investigation."

You left out an important condition. That is, not disproved AND uniquely consistent with the available evidence.

"If I am sitting on a jury as a person that has not specific knowledge about fire investigation, and you tell me you can never prove a hypothesis to be correct you have just lost me. My question would be why you made me sit through your testimony if you cannot tell me which hypothesis is correct. According to science you may be correct, but you are just waisted my time. If I’m already with the opinion that I did not want to be on the jury, you are saying that you cannot say which of the hypotheses is correct will aggravate me more. From there I will just discount what you have to say."

Sometimes your job as an expert testifying in court is to explain how science works, what it can and cannot do, what is the goal, what is reliability, and how did you apply the SM in a reliable manner? As an expert, you should know that the concept of science is somewhat foreign to juries or the layperson is ignorant of such. You need to educate the jury as opposed to compensate your testimony to meet their ignorance. Most of the time, you are educating your client/lawyer on these issues, but it still may need to be addressed in your trial testimony.

"As the person sitting on the jury there are only two possibilities. The first is you know what happened or the second is you do not know. You may say your profession has four outcomes, but all I what to know is which of your hypothesis is correct to explain what took place..."

It is not the profession that has four outcomes, it is the application of the SM that has four outcomes, as previously described. Science cannot tell you that your are "correct." That is why reliability is so critical. As an expert you should have to describe how you arrived at your determination by application of the SM.

"If you say most reliable, then I want to hear about the others you consider reliable."

Certainly. You can walk through your application of the SM in a specific incident and how you used the available evidence.This can be done with your client, your expert report, and/or deposition and trial testimony.

"If you say there are none that are reliable, then I want to know why you used the term “most reliable”."

Not sure I have ever said that "none are reliable." None [hypotheses] may be uniquely consistent with the available evidence Valid hypotheses (formulated with evidence) that cannot be disproved (with additional evidence) are still reliable (use of evidence, rather than lack of evidence, which is unreliable). It is the final determination that is the most reliable. "Undetermined" can also be the most reliable determination that can be made with the available evidence.

Douglas J. Carpenter, MScFPE, CFEI, PE, FSFPE
Vice President & Principal Engineer
Combustion Science & Engineering, Inc.
8940 Old Annapolis Road, Suite L
Columbia, MD 21045
(410) 884-3266
(410) 884-3267 (fax)
www.csefire.com