The whole is not always the same as its parts

You are going to buy a new home.  The house is 2000 square feet on a 3/4 acre lot.  You hire Rich (the termite inspector) to check it out before you buy. After all, no one wants to buy a house with termites. 

  • Good news!  The house passed.  No termites.  Thus, you buy the house.
  • Bad news!  A month after the sale closes you discover - termites.  

What?  How could this happen?

 
You go back and look a little deeper in the method of inspection Rich relied upon.  You find out his methodology was to only check "one square inch" of the floor in the house.  When he did not find anything wrong within the "one inch" he assumed everything else was also termite free.
 

How do you feel now?
 
A part of something does not always represent the whole. Determining how many termites are in "one square inch" of a house does not really answer the question whether you have a termite problem.
 
The termite inspector committed what logicians call the all things are equal fallacy.  This occurs when when it is assumed, without justification, that conditions have remained the same at different times and places.
 
The same danger is present when attempting a forensic measurement.  For example, in a typical DUI case where a blood sample is taken, the lab will test less than a M&M size sample of blood.  However, in Arizona the legal definition of an alcohol concentration is grams per 100 micro-liters. Translation, the legal definition of an alcohol concentration requires multiplying the results of the "one inch" by about 1000 (assuming the M&M is about 100 micro-liters).
 
The danger is assuming the rest of 1000 micro-liters (or 100 milliliters) has a proportional amount of ethanol in it.  Small errors multiplied by 1000 can easily mislead you to believe that a person's alcohol concentration is above a legal limit when it is not.
 
Like the termite inspection, it is up to the crime laboratory to prove their justification for assuming using such a tiny amount below the legal definition of an alcohol concentration answers the question - is the person above the legal limit?  After all, no one wants termites...or people being wrongfully convicted.
 
 

The Supreme Court Splits the baby in the Scottsdale Crime Lab Cases.

The highly anticipated Arizona Supreme Court opinion regarding the Scottsdale Crime Lab scandal was issued yesterday.   In a very Solomon like decision, the Court granted both sides some relief.

 

The decision contains a lot of legal nuance requiring explanation. Here is a summary and a few thoughts:

 

Admissible Is Not The Same As Reliable

 

While the Court decided the blood alcohol measurements are admissible - they did not hold they are reliable. There is a big difference.  As a matter of fact, the Court expressed its concerns with the Scottsdale Crime Lab's "shaky" evidence. 

 

The Court merely held the prosecution may present the blood alcohol measurements to a jury and argue they are reliable.  The jury will make the final decision.

 

This standard is similar to a finding there was probable cause for a person's case to proceed to trial.  However, at trial, the same evidence will now need to exceed a much higher threshold - beyond reasonable doubt.

 

What Effect Did Yesterday's Decision Have On The Lower Courts' Rulings?

 

There were two lower court rulings: (1) the trial court's ruling suppressing the evidence; and (2) the Court of Appeals ruling reversing.

 
The Arizona Supreme Court vacated the relevant portions of the Court of Appeals decision and the trial court's ruling.  It then issued a new opinion which provided additional guidance on the admissibility of scientific evidence in a jury trial.
 
The Legal Boundaries Of The Supreme Court's Decision.
 
A few years ago, Arizona adopted something called the Daubert standard for the admission of scientific evidence. This was reflected by an amendment to Rule 702 of the Arizona Rules of Evidence.
 
The Court's holding here was limited to only one of the requirements of Rule 702.  Specifically the ruling is limited to subsection (d) of Rule 702, which focuses on the reliable application of a methodology to the facts.
 
What Did Each Side Get Out Of The Supreme Court's Decision?
 
The prosecution avoids mass dismissals of cases where they claim a driver was impaired, but now they have to persuade a jury in every case that the crime lab's forensic malpractice does not matter.
 
The defense is primarily benefited in two ways: (1) the right to present all the evidence of the crime lab's malpractice is firmly established; and presumably (2) the right to obtain evidence of software malfunctions and errors from the crime laboratory also appears to be affirmed. 
 
The Court's acknowledgement that the evidence presented at the 17 day pretrial hearing was both relevant and admissible at trial, implicitly holds that the defense has a right to this evidence in discovery.  This is a significant change.
 
The majority of the evidence presented to the trial court by the defense was not provided by the prosecution.  It was obtained through the collaboration of the defense community and through requests made pursuant to Arizona's public records laws.  
 
Moreover, before the pretrial hearing, there was a court order requiring the Scottsdale Crime Lab to provide the defense with all the data produced in 2011.  They were given a significant amount of time to comply, but did not even attempt to gather the information. Instead, the prosecution appealed the order, and the Arizona Court of Appeals reversed.  
 
The prosecution convinced the appellate court that the defense was merely on a "fishing expedition."  However, in hindsight, it turns out there were some pretty big fish in the pond. We can only imagine what we would have found if the yesterday's opinion had been in place at that time.
 
The holding also appears to clear the way for the defense to present a jury with evidence of the hundreds of catastrophic software malfunctions resulting in unreliable and misleading evidence.  The jury may now discover, that for years, the lab hid this damming evidence.  They may hear of internal crime lab emails from analysts admitting to deleting "incorrect results." 
 
And yes, prior to this decision, the prosecution vigorously argued the jury should not hear this evidence.
 
Does This Decision End The Debate Over The Scottsdale Crime Lab's Forensic Malpractice Issues?
 
Nope.
 
The issues will continue to be litigated - one case at a time. However, we now have some new rules of the road that empower the defense to present their case.  
 
In Sum
 
...the decision means we can't shop for justice at Costco. While there will not be a bulk dismissal of consolidated cases, we still get to present these issues one case at a time...jury by jury. 
 
This could take a while.
 
RELATED:
 
 

Arizona Supreme Court: Scottsdale Crime Lab Update

Tomorrow around 10:00 a.m. the Arizona Supreme Court will issue its decision regarding the Scottsdale Crime Lab.  Here are some of the new stories about the case of STATE v HON. BERNSTEIN/HERMAN:

I will provide a summary of the Supreme Court's opinion following its release.

Lawrence Koplow

Measuring and Counting

 MEASURING

Measuring is the assignment of a number, and all the uncertainties of that of that number, to something.  The purpose of assigning a number is to give meaning to the object measured.

  • Uncertainty: A bag placed upon a scale shows its weight to be 41 pounds.  If the bag must be less than 50 pounds, then the number produced by the scale indicates it meets this requirement.  However, you must know how far from its true value might the 41 pound number be off by?  Uncertainty is the amount of doubt (e.g. the amount of possible variation) you should expect that number might be off.
  • Fit for Purpose: Assume there are two scales.  The same bag weighing 41 pounds is place on both scales.  However, it was determined that Scale A produces numbers that can be off by as much as 30 pounds.  It was also determined that the number produced by Scale B merely off by as much as 3 pounds.  Knowing the amount of uncertainty contained in the number helps distinguish counting from measuring.  Knowing the uncertainty allows you determine if the measurement is fit for the purpose of determine if the object exceeds 50 pounds.

Measuring relies upon estimation.  The choice of data, the methodologies employed, and level of quality measures used tells you how confident you can be in the estimation.  Once you have a reliable estimation of how close a number may be (or not be) to the true value, you can make informed decision as to what purposes the number can be used - and not used.  

 

COUNTING

Counting is not the same as measuring.  However, the two are often confused.  Counting is usually a technique within a measuring process (methodology).  Counting can result in an exact number.  However, measurement will never claim to represent a true value. Measurements are merely estimations.

Counting an exact amount of something is often not possible or practical.  The thing you are intending to measure (the measurand), the matrix it is found in, or the level of accuracy required may make counting impossible.   Thus a system is needed to provide a reliable estimation which you can rely upon.  

Some things to take into account when making an estimation:

  • Distinguishing: Some molecules are so similar to others that it is often impossible continuously distinguish them from each other.  Thus, they cannot be easily counted.
  • Location: Some substances are contained in places we cannot practically enter to count them.  The best way to know how much alcohol is affecting a person's brain at a particular time would be to take a sample of brain tissue.  However, society has not yet determined such a procedure falls outside the protections of a person's 4th Amendment rights.
  • Gas Chromatographs: The results of a gas chromatograph are often used to determine whether a person's alcohol concentration is above a legal limit in DUI cases.  However, the machine does not measure a person's blood alcohol concentration.  If properly used, the machine merely counts the number ethanol molecules in a gas portion of a headspace vial.  Thus, it indirectly counts a microscopic amount ethanol from a tiny sample.  

A measurement based upon a machine's indirect count of a substance results from combining it with algorithms, numerous assumptions, and historical data regarding the past performance of the machine (and software) used in the process.  This is known as an uncertainty calculation.

In this manner, measuring requires much more than counting.  Measuring requires more than merely assigning a number to an object.  More importantly, one can assign a number to an object but not create a measurement.  When this occurs it is not a measurement.  It is a misrepresentation.

 

Counting is what you do to get a number.  Measuring is what you do if you want to know the truth about the number.

Scottsdale Crime Lab: The Supreme Court's Statement of Issues

Today at 11:00 a.m. the Arizona Supreme Court will hear oral arguments regarding whether to reinstate a trial court's finding that - blood alcohol measurements created by the Scottsdale Crime Lab are unreliable.  You can read a history of this litigation by clicking here.

A case being selected by the Supreme Court for review is a rare event.  Simple math shows it is unlikely that any particular case will be reviewed by the Arizona Supreme Court.   The Court receives a substantial amount of “Petitions” to review lower court decisions, but it only selects a small percentage of them each year.  However, because the issues in this case (it is actually a consolidation of 11 cases) will have wide-ranging consequences, it was an ideal case for the Court to review.  The final ruling by the Court, regardless of who prevails, will likely affect how scientific evidence will be handled by Arizona courts for years to come.

While both parties have their own opinions as to what the key issues are, the Court will provide a summary and statement of the issues from their perspective prior to the oral argument.  Last week, as expected, the Court issued its written statement.  Below are the issues as stated in the Court’s summary:

 

1. Did the Court err by holding that Rule 702(d) challenges are excluded from judicial gatekeeping scrutiny under Arizona law?

 

2. Did the Court err in using the accuracy of the results as the criteria for a gatekeeping analysis instead of using the trustworthiness of the methodology used to generate the results?

 

3. Did the Court err in substituting its own judgment for the trial court’s without finding that the trial court’s decision constituted an abuse of discretion?

 

After reading this statement of the issues, one could jump to a conclusion from the way the issues are framed, that the Court is leaning in a particular the direction.  A word of caution – no one knows how the court is leaning.  The Court’s final opinion could easily list a different set of issues.

Today’s oral argument is being held at Arizona State University Law School.  The argument is open to the public and starts promptly at 11:00 am.  Everyone is welcome to attend – regardless of which side of the argument you are on.

The anatomy of a gas chromatograph

 

The results produced by a gas chromatograph are usually the difference between innocence and guilt in a DUI case.  The prosecution’s purported blood alcohol concentration (BAC) is typically the “end-all be-all” of their case. Let’s take a look at how this machine creates such a critical measurement.

Big Pictures Thoughts

  • If done properly, gas chromatography is a reliable way to measure the amount of blood in an alcohol sample.  However, automobiles are also reliable, but there are still thousands of car wrecks every day.  There is no presumption of reliability simply because a gas chromatograph was used.
  • The measurement process has both human components and machine components.  All steps in the process must be done correctly for the measurement to be trusted.
  • The goal of is to produce a measurement, which is both accurate and reliable.

General Principles

  • Gas chromatography is an indirect measurement.  The machine does not test liquid portion of a blood sample.  In headspace gas chromatography, the machine converts substances to a gas, and then it must separate the different types of molecules in the sample.  After separation, a microscopic amount of the gas is measured by software.
  • The machine must demonstrate it is able to separate different types of molecules before it can measure them.  If it cannot properly separate different categories of molecules, then its measurements may be artificially higher.
  • Gas chromatography is done in manner like a production line.  Multiple samples (usually over 100 vials) are being processed in a “batch.”  It is essential to safeguard against the wrong information being assigned to the wrong sample.

Vocabulary

  • Gas chromatograph - a machine that separates molecules, and then measures, the amount of the various components in a sample.
  • Gas Chromatography - the scientific process performed by a gas chromatograph.
  • Chromatogram – the graphical representation of the data produced by the gas chromatograph.  This is where you will find the final measurement.  A chromatogram is the machine’s conclusion.

The Human Part

The measurement process starts long before the gas chromatograph is actually turned on.  The blood must be collected, identified, stored and transferred properly before the sample is put into the gas chromatograph.  Even the best machines cannot account for, or identify, that a sample has been corrupted.  The principle of garbage in garbage out must be kept in mind.  That is, incorrect (or poor quality) input will always produce wrong output.  

Human are also responsible for teaching the machine a specific alcohol concentration.  The machine does not come out of the box knowing any specific alcohol concentration.  Typically a lab will purchase approximately four (4) different alcohol concentrations from a vendor.  For example, .01, .10, .20, .40 are often used to calibrate the machine. 

These samples are put into the machine and the analyst programs the machine’s software to use these values.  If the analyst tells the machine a sample is a .40 but it is really a .30, the machine cannot tell the difference.  Ensuring a calibrator is what it purports to be is known as traceability.

The Machine Part

The machine starts its analysis after a small portion (less than the size of the a single M&M) of each blood sample is put into a headspace vial. The headspace vials (usually over 100) containing the samples are loaded into a part of the machine called the autosampler.  

The samples are then heated (in a headspace tube) forcing molecules in the liquid portion of the sample to rise.  After the molecules are vaporized, a needle punctures the top of the headspace vial and extracts a microscopic portion of the gas above the liquid.

These vaporized molecules are pushed through long thin columns by a carrier gas (hydrogen or helium).  These thin columns have a chemical coating inside them designed to interact with the molecules passing through them.  The carrier gas moves at a constant pressure.  This results in different molecules in the gas to group together (e.g. ethanol with ethanol, methanol with methanol).  Each molecule group, such as ethanol, has a unique rate of speed.  This accounts for the separation of the each substance in the columns.

After each molecule group is pushed out of the column, they will be pushed to a detector.  The time when is substance exits the column is called the time it elutes.  The detector’s software has been programmed to identify different substances by the time they elute from the column.  The Flame Ionization Detector, as the name implies, then burns each molecule group and then measures how much is burned.

The software gathers the “raw data” and then processes it.  The “process data” is graphically represented in something called a chromatogram.    The measurement is found here.

The above summary just scratches the surface of the measurement process using a gas chromatograph.  If you are going to rely upon the measurement produced by this technique, then every step in process (both the human and machine) must be shown to have been done correctly.