Friday, October 27, 2017

Forensically sound

"Is it forensically sound?"

I've heard this question asked many times since I began working in forensic analysis many years ago. Me being me, I wanted to know what it meant to be "forensically sound." Here's what I found as I took a journey through the English language.

"Forensically." The root of this is "forensic."


The root language for the English word "forensic" is the Latin "forensis." It means a public space, a market, or in open court.


Forensis means "of or pertaining to the market or forum." Another way of looking at this can be, activities that happen in the market, forum, public space, or open court.

Ok. We've got "forensically" down. What about "sound."



Sound, from the Old English, means that which is based on reason, sense, or judgement, and/or that which is competent, reliable, or holding acceptable views.

Put together, and given the context of our work, "forensically sound" can mean that activity, related to work for the court / public, which is well founded, reliable, and logical - which is based on reason, sense, or good judgement.

Great, we've now got a working definition. Now how does it apply to our efforts?

In the US, the Judge acts as the "gatekeeper." In providing this "gatekeeper" function, the Judge should weigh the foundation and reliability of the evidence being submitted in the particular case. When questions arise as to science, validity, and/or reliability, either party can ask the Judge for a hearing on the evidence and explore these issues (i.e. Daubert Hearing).

One of the ways that Judges evaluate the work is by comparing the work product to known standards. In our discipline,  we can find standards at the ASTM. For image / video processing, the standard is ASTM 2825. Taking a step back, standards are "must do" and guidelines are "may do."

Thus, if you've followed ASTM 2825 (meaning your work can be repeated), and you use valid and reliable tools, your work is "forensically sound." It's a two part evaluation - you and your tools.

Did you work in a valid, reliable, repeatable, and reproducible way? Are your tools valid and reliable? If the answer is yes to all of these, they your work is forensically sound.

In the many times that I've been asked to evaluate another person's work (i.e. from opposing counsel), this is the standard with which I work. It forms a checklist of sorts.

  • Do I have the same evidence as the opposing side? (i.e. true/exact copy)
  • Is there a written report that conforms to ASTM 2825-12? This assures that I can attempt the tests and thus attempt to reproduce their results. 
That's really it for me. Others may concentrate on training and education and certifications. I really don't. If they aren't trained / educated, it will show in their reporting. To be sure, there are avenues to explore if you have the other person's CV (verify memberships, certifications, education etc.). But, I would hope that folks wouldn't embellish their CV. It's so easy to fact check these days, why lie about something that can be easily discovered via Google?

You have a copy of the evidence and the opposing counsel's report. You attempt to reproduce the results. Two things can happen.
  1. You successfully reproduce the results and come to the same conclusion.
  2. Your results differ from that of the opposing counsel.
If the answer is #1, you're finished. Complete your report and move on. If the answer is #2, can you try to figure out the errors? Your report may include your conclusions as to what went wrong on the other side and why yours is the correct answer. 

I hope this helps...

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