Guest Blog Post From Dr. Frederic Whitehurst PhD JD: Circuitous thought-the myth of reliable and valid marijuana identification in the courtroom

Circuitous thought-the myth of reliable and valid marijuana identification in the courtroom

By:  Frederic Whitehurst, J.D., Ph.D. [1]

As scientists we all agree that the hallmarks of science are validity and reliability. What do we mean by that? Well, the government scientist has to agree that his method of answering a question put to him has to be valid and reliable. So no matter how he identifies marijuana that method must be valid and reliable. Scientists determine validity and reliability with data. What does validity mean? It means that the method we use to answer a question must appropriate for the use to which we put it. Better said, just because we have a hammer does not mean everything is a nail.

The question we are asking about marijuana is “Is this material marijuana?” That means is it marijuana to the exclusion of all other plants? So we have to have a protocol that will show us that the material we have is marijuana to the exclusion of all other plants. In order to show that our protocol is valid we must either have tested all other plants or have a theoretical argument as to why no other plant can be mistaken for marijuana using our protocol. The only attempt at validation that has been conducted in the past is the work of George Nakamura and John Thornton back in the early 1970’s. That did not show the protocol identified marijuana to the exclusion of all other plants but only tested the protocol on 31874 plants. So no one has validated the protocol. The government scientist can not show that. In a Frye state we accept the opinion if the method used to arrive at it is accepted by the community of peers. The community of peers do not accept that the marijuana analysis protocol is valid because no one has validated the protocol. They just use the method. No one has validated it. As for reliability, that means if the tests is performed by one person many times or by many people will one get the same answer. However, there are no reliability studies known. Government scientists simply say that they always get the right answer and never have gotten the wrong answer but they are not being tested for reliability with known standards. They are simply saying that the unknowns must be marijuana because the police say they are marijuana so they must be marijuana.

Circuitous thought. Wrong thinking. Compound that with the paucity of scientific data that exists to test the reliability hypothesis and you have nothing to refer to to indicate that the protocol is actually reliable. So the peer group would agree that in order for the protocol to be used it must be shown to be valid and reliable and it has not been shown to be so it can’t be used…but they use it anyhow.


[1] Executive Director, Forensic Justice Project, Washington, D.C., B.S. Chemistry, 1974, East Carolina University, Ph.D. in Chemistry, 1980, Duke University, J.D., 1996, Georgetown University School of Law. (202)342-6980.

Leave a Reply

Your email address will not be published. Required fields are marked *