The Friction Ridge
Written by John P. Black, CLPE, CFWE, CSCSA   

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EVERY SINGLE DAY, fingerprint examiners routinely and reliably determine that questioned friction ridge impressions possess sufficient information to identify to a known source. These sufficiency determinations are made based on the quality and quantity of information available in an impression, as well as the ability, experience, training, and visual acuity of the examiner.

Although there is currently no generally accepted standard for sufficiency in the fingerprint community, examiners trained to competency can—and do—reach valid conclusions that are supported by physical evidence and will withstand scientific scrutiny.

Friction ridge examiners can typically discuss their examinations and results among colleagues without any difficulty. This often is not the case, however, when the discussion involves the concept of sufficiency. As a result, it may also be difficult to explain this concept to non-practitioners, such as jurors, judges, and attorneys.

What makes this problematic is that the non-practitioners mentioned above—particularly jurors and judges—often make crucial decisions based on the information they receive. If they don’t understand how friction ridge examiners can reliably determine sufficiency, then they don’t have all the information they need to make an informed decision. With this in mind, several analogies are offered below for helping non-practitioners understand the concept of sufficiency.

  • Teachers routinely test students to determine if they have a sufficient understanding of the course material. Teachers are able to do this based on their training and experience in testing numerous students over a long period of time. They can reliably determine whether the students have truly grasped the material, or if they have simply memorized and regurgitated the information for test purposes.
  • Mechanics typically perform leak checks after patching damaged tires. Once the patch is applied and the tire re-inflated, the mechanic will apply a soapy solution to the patch area and subsequently look for any air bubbles around the patch. If no air bubbles are observed, then the mechanic determines the patch job is sufficient and that the tire is safe to put back into service. This decision is governed by the mechanic’s training and experience in patching many tires over time.
  • Farmers must constantly monitor their crops to determine if they are providing sufficient water, fertilizer, and pest-control methods to ensure a successful harvest. Again, their decisions regarding the quantities needed by the plants are determined largely by the experience of the farmer.

Now, the reader may be thinking that these analogies are very simple and seem to have nothing to do with friction ridge examination. Hopefully, however, it will be recognized that these are attempts to explain the concept of sufficiency, as well as to show that sufficiency exists in other professions. More important, these analogies show that sufficiency determinations made in other professions are typically based on a person’s training and experience. Why would it be any different for friction ridge examiners?

It doesn’t matter if an examiner is determining sufficiency for an initial value assessment or if the sufficiency determination is for the purpose of making an identification. What does matter is that the examiner draws on his/her experience with numerous impressions, over time, to assess the quality and quantity of available information in making these sufficiency determinations.

Besides, it would not be surprising if a teacher, mechanic, or farmer is in the jury box during your next trial. They will likely have sufficient understanding of the analogies!

About the Author

This e-mail address is being protected from spam bots, you need JavaScript enabled to view it is a Senior Consultant and the Facility Manager for Ron Smith & Associates, Inc. in Largo, Florida.


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