Point Of View: Distortion vs Dissimilarities

[Charles Parker]

POINT OF VIEW: THE FOUR D’S OF LATENT PRINT ANALYSIS

There has been some discussion lately about distortion and dissimilarities and there is a new site on CLPEX that offers images of distortion or dissimilarities. You get to pick which one it is.

I am fairly sure that this concept of distortion and dissimilarities comes from an article by William Leo of California in the JFI (Vol. 48 #2, 1998). This same use of words was brought up at a SWGFAST meeting a number of years ago and there was some good discussion about those two words and another one called Discrepancy. And from looking at the SWGFAST Glossary they kind of kept in line with Mr. Leo.

Now I have nothing against Mr. Leo’s article. It is a fine article and does bring up some issues that certainly needed to be addressed at that time and probably still do today. My point of view in this posting is the way the words are used. Maybe it is a regional thing that Distortion and Dissimilarity are used together while the way I was trained they were not. So I will now endeavor to put forth the four D’s as it was explained to me a long, long time ago.

Disruption--This refers to the original friction ridge skin and can be caused by genetics (dysplasia), disease (leprosy), or physical (scars or amputations). Disruptions caused by disease or physical means can be permanent or on some occasions temporary. These types of disruption of friction ridges can be transferred to surfaces. Sometimes they are seen in latent prints as blank areas or their visible design may transfer.

Distortion--This generally refers to a physical change in the appearance of the friction ridge detail as it comes into contact with a surface, but can also be caused by some physical action against the latent print after contact. Some factors to be considered in distortion is the material on the friction ridges (matrix), the surface being touched (substrate), the movement of the friction ridge detail (pressure, slippage, compression, rotation, overlay, reversal, displacement, etc), other contact with the surface after the friction ridge detail was left (moisture, rubbing by another item, etc.), the developing medium (physical, chemical, or dye), or the type of preservation (tape, rubber or other lifters).

Dissimilarity--The root word is similar. Latent prints from the same source may appear to be dissimilar. There is a noted difference or a point of difference (ending ridge on one, bifurcation on the second). If you have an area or point between two prints that do not appear to be similar but can be explained by an aspect of distortion or in some rare cases an effect of disruption then they can be from the same source.

Discrepancy--This refers to a disagreement which cannot be explained. If on one print you have a bifurcation with three ending ridges between it and the next feature, while on the second print you have a bifurcation with five ending ridges between it and the next feature, and you cannot explain this disagreement then you have a discrepancy.

These are the four D’s as I was taught, but since SWGFAST has decided that Discrepancy and Dissimilarity have the same meaning then I am simply writing this as my point of view.

I would also like to bring out in Mr. Leo’s article that in the beginning he list two sources A. Moenssens “Fingerprint Techniques”, and R. Olsen “Scott’s Fingerprint Mechanics”. In his introduction he states “…in order to have a valid identification, the print in question must be void of any dissimilarities.” And then he goes on to quote the two sources.

Now Moenssens and Olsen do not use the word “void”. Moenssens goes like this “…., without unexplained dissimilarities. Many dissimilarities between latent and inked prints can be explained, so they are insignificant”. While Olsen’s book states “The absence of unexplainable dissimilar characteristics in a fingerprint is essential for positive identification, but sometimes a characteristic may appear dissimilar to the layman and can be satisfactorily explained by a qualified examiner ….”. Now as I understand those two quotes, a dissimilarity can be explained. I wonder why SWGFAST gave Discrepancy and Dissimilarity the same definition?

Now I usually abhor using definitions out of dictionaries because they are set up for common usage, and even they will generally say somewhere in their preface, that they cover definitions for the majority of people in everyday situations. They may not cover specialized definitions. I have never seen a dictionary provide the definition of a tented arch or an ulnar loop. But since that is the thing to do sometimes, I am providing definitions from my dictionary, the New College Edition of The American Heritage Dictionary of the English Language of 1978.

DISRUPT—To upset the order of OR Throw into confusion or disorder.

DISTORTION—Applies to the physical change in shape.

DISSIMILARITY—The quality of being (having) distinct or unlike differences. 2. A point of distinction or difference.

DISCREPANCY—Divergence or disagreement, as between facts or claims. Not consistent or matching.

Disruption and Distortion are used to describe cause and effect.
Dissimilarity and Discrepancy are used to describe an observation.

My point of view is that Dissimilarity and Discrepancy are not one and the same idea and should not be considered as the same definition.

I want to repeat that I am not bashing Mr. William Leo. He has written some outstanding material and I for one agree with most of what he has written. However this regional use of terms is what I am trying to put forth, and not that Mr. Leo is wrong from a California perspective.

Your input, comments, or critique are welcome.

[CHERIM22]

Hello,
You caught me at the right time with this topic, I was just doing some reading about this the other day. I came accross several articles discussing the difference (ha, another "D" word) between dissimilarity and distortion. It is funny when I was first being trained I was taught to say I make a comparison by comparing the information and it's relative position in one print to an other print..bla blah, but it always ended up with "without any unexplainable dissimilarities". Well, that was a few years ago, and things change I guess. These newer articles said to remove dissimilar from my explanation because it means DIS-similar = not the same. So you can't say on one hand that it is a match and then turn around and say I can explain the "dissimilarities" (the fact that it is not a match). It was all a little confusing initially. So I will just testify to distortions and individualizations and stay away from that mess
I appreciated your post though, I hadn't even factored in "disruption" - thanks!