Doug:

I agree that we use a level of certainty “implicitly” is thought to be part of the scientific method. Meaning that something is implied, rather than expressly stated. My disagreement with this word is that it also has the meaning of something being unquestioning, unreserved, or unconditional. In reaching and explaining one’s conclusion I believe explicitly is used in that one clearly expresses, demonstrates, or formulates an opinion.

Your answer to my second question directly relates to the level of certainty. You are correct there are no absolutes. That means any opinion rendered is based on reliable knowledge while knowing there is always the potential of it being proven wrong. This is a level of certainty base on what is known at the time the opinion is given.

So, what you are saying is what we get from using science to determine the cause of an incident is the best science can do at that time.

I am just saying I believe that using science to test a hypothesis there is the potential that there may be multiple hypotheses that cannot be disproved. At that point I can evaluate the evidence and say on of the hypotheses have a greater probability of being the cause over the others and then list the facts to support this opinion. What I must also do is be willing to agree that even thought I believe this one has the greatest potential, I cannot eliminate the fact that one of the others could be the cause. Here I am using the level of certainty but also explaining its use. Then it is up the trier of fact to make the final determination based on the evidence presented.

I believe judges and juries, when presented with two different opposing set of facts, use the level of certainty by weighing what they were told by each side and then saying which was the most probable.

Because there is as you say no absolutes in science, there needs to be some level of certainty in a scientific conclusion.

I guess what I am against is that information keeps being taken out of NFPA 921 in one section where they keep using it in another. As an example, the document took out negative corpus. They said it is wrong to use negative corpus to reach a conclusion. At the same time, they leave the process in the text of other sections and say it is acceptable to be used. They took out the chapter on classification but instructed the user in other sections that they should give a specific classification. They are doing the same thing with the removal of level of certainty. They take out the level of certainty but leave in the document instructions that if there are other hypotheses the are consistent with the data the investigator should list the facts that support his cause determination over the others. They even tell the user how to us the level of certainty. The committee is sending mixed messages.

Jim Mazerat
Forensic Investigations Group