People mistake readability with trueness all the time. Imagine a full-sized live elephant gets on scale. The scale reads “113 pounds.” Not a single one of us would have any difficulty rejecting that measurement. We intuit that it is wrong. Really wrong. It’s not feasible. It’s not plausible. There is no way it could be. […]
The testing of unknowns-what is confirmatory testing?
When testing unknowns, we are doing precisely that. We will never know the true CONTENTS (in terms if a qualitative measure) of the sample, let alone the true value of the contents (in terms of the quantitative measure). By definition, all testing is about the tester’s willingness to accept the risk of being wrong most […]
Why Don’t we Six Sigma Forensic Science? It’s all about method validation, traceability, and quality assurance
The goal of any form of identification or quantitation is to produce a specific and true expression that is valid. In the forensic world how we scientifically arrive at a reported result should not be an act of mysterious busywork, but rather a result of planned, purposeful meaningful action that is validated and truly scientific. […]
Guest Blog Post From Dr. Frederic Whitehurst PhD JD: Cry Foul. Cry Foul. The Statistician Approaches
Cry Foul. Cry Foul. The Statistician Approaches-An Original Poem by Dr. Frederic Whitehurst By: Frederic Whitehurst, J.D., Ph.D. [1] Cry Foul, Cry Foul The Statistician Approaches Young maidens lift not your eyes To gaze upon the Gaussian Wizard Lest your notions of the perfections of God’s universe Be dashed upon the rocks of the Realization […]
Zero is not a valid data point for calibration purposes
When the quantitative measurement really matters to determine guilt, we have to understand how that measurement is achieved. In the case of the analysis of biological samples that are tested, quantitation of an unknown is derived from a calibration curve. The proper construction of the calibration curve is a crucial component of quality control. It […]
Quality Control in GC-FID: Teaching the machine right from wrong
It is shocking but very true statement that most sophisticated instruments such as a Gas Chromatograph (GC) with various detectors whether it is a mass spectrometer (MS) or flame ionization detector (FID) when produced and manufactured are incapable of producing meaningful results “straight out of the box.” These machines have to be “taught” what it […]
How the GC-FID arrives at a quantitative result: Auto-integration versus Manual Integration
A frequently asked question on the listservs that I belong to basically asks the following question: In GC-FID use to quantify Blood Alcohol Content where EtOH is the target analyte, how does the machine arrive at the reported number? The machine is called a Gas Chromatograph with a Flame Ionization Detector (GC-FID). Typically the sample […]
More on metrology in the courtroom
A good colleague and friend of mine, Ted Vosk introduced me to the world of metrology in the courtroom in 2008. He has introduced a lot of us to it. Since then I have learned more about metrology, statistics and validation having taken a lot of courses and having read a lot of materials on […]
Standards, Controls, Calibrators, and Verifiers, Oh my…
Lions and Tigers and Bears… Verifiers, Calibrators and Controls… Oh my! Sometimes a criminal defense attorney can at times feel like Dorothy in the Wizard of Oz in that we are transported from the relative safety of home (the courtroom) to the weird world of Oz (the laboratory). There are unusual and often times conflicting […]
Why single column Gas Chromatography-Flame Ionization Detector analysis is not forensically or scientifically acceptable
There is a large difference between a single column analysis and a dual column analysis when it comes to the ability to most correctly identify and quantitate an unknown in the scientific world. In forensic science, we are constantly testing unknowns. What is meant by this is that we have a sample that is seized […]
Why evidentiary breath test machines are not regularly scientifically calibrated
One of my favorite movies is The Matrix. There is one scene that really jumps out to me. When Morpheous and Neo first meet. Morpheus shows Neo two pills: a blue and a red one. If Neo chooses the blue pill, he will wake up in his bed and forget about everything that happened to […]
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