The 2016 Utah IAAI Seminar in Wendover, Nevada:
February 21-24, 2016
Negative Corpus vs. the Process of Elimination
Here are some relevant excerpts from the 2014 edition of NFPA 921 regarding testing of a hypothesis, the process of elimination and negative corpus:
4.3.6* Test the Hypothesis (Deductive Reasoning). The investigator does not have a valid or reliable conclusion unless the hypothesis can stand the test of careful and serious challenge.
Testing of the hypothesis is done by the principle of deductive reasoning, in which the investigator compares the hypothesis to all known facts as well as the body of scientific knowledge associated with the phenomena relevant to the specific incident.
A hypothesis can be tested physically by conducting experiments, analytically by applying accepted scientific principles, or by referring to scientific research. When relying on the research of others, the investigator or analyst must ensure that the conditions, circumstances, and variables of the research and those of the hypothesis are sufficiently similar.
Whenever the investigator relies on research as a means of hypothesis testing, references to the research relied upon should be acknowledged and cited. If the hypothesis is refuted or not supported, it should be discarded and alternate hypotheses should be developed and tested. This may require the collection of new data or the reanalysis of existing data. The testing process needs to be continued until all feasible hypotheses have been tested and one is determined to be uniquely consistent with the facts and with the principles of science. If no hypothesis can withstand an examination by deductive reasoning, the issue should be considered undetermined.
184.108.40.206* Any hypothesis that is incapable of being tested either physically or analytically, is an invalid hypothesis. A hypothesis developed based on the absence of data is an example of a hypothesis that is incapable of being tested. The inability to refute a hypothesis does not mean that the hypothesis is true.
19.6 Testing the Cause Hypothesis. Each of the alternate hypotheses that were developed must then be tested using the Scientific Method. If one remaining hypothesis is tested using the “scientific method” and is determined to be probable, then the cause of the fire is identified.
19.6.5* Appropriate Use. The process of elimination is an integral part of the scientific method. Alternative hypotheses should be considered and challenged against the facts. Elimination of a testable hypothesis by disproving the hypothesis with reliable evidence is a fundamental part of the scientific method. However, the process of elimination can be used inappropriately.
The process of determining the ignition source for a fire, by eliminating all ignition sources found, known, or believed to have been present in the area of origin, and then claiming such methodology is proof of an ignition source for which there is no supporting evidence of its existence, is referred to by some investigators as negative corpus. Negative corpus has typically been used in classifying fires as incendiary, although the process has also been used to characterize fires classified as accidental. This process is not consistent with the scientific method, is inappropriate, and should not be used because it generates untestable hypotheses, and may result in incorrect determinations of the ignition source and first fuel ignited. Any hypotheses formulated for the causal factors
Misunderstandings about the nature and content of National Fire Code© NFPA 921 - Guide for Fire and Explosion Investigations abound in the fire investigation industry. These “Myths and Mysteries” tend to depreciate the value of the document, especially among those who need its guidance the most. This is caused by failures to understand and appreciate the nature of the NFPA consensus code promulgation system, the history of the fire investigation profession, the nature and history of NFPA 921 itself; and even semantics. This presentation is designed to expose and explain what the ill-informed see as the “myths and mysteries” and perceived shortcomings of this seminal document. One of the three, still serving, original Technical Committee on Fire Investigations members discusses the most common and controversial misunderstandings and misconceptions about NFPA 921.