CLPEX Chat Board

Anyone have a good set of pictures to illustrate significant intra-source varation -- two good-quality rolled prints or two latents known to be from the same person that might trip up a trainee (or even a veteran)? I'm looking for something for an article and/or powerpoint to help attorneys understand what I mean when I talk about intra-source explainable differences.

You might want to take a look at the FIGS on the Home Page.

Thanks! Are these known matches created for training purposes, or those which an examiner has concluded are matches in casework? If the latter, any dispute by the identified person that they are the source?

All of the FIGS were created for training purposes as interesting comparisons with the primary purpose to show some stated effect of Distortion (Intra-Source Variation) or Friction Ridge Disruption (present on the friction ridges prior to and after contact with a surface—where Distortion is some effect from the contact). There are a few that are offered as just plain interesting. Most can be determined to be a match. Some are not and that is why all are offered as interesting comparisons.

They are perfect for power points and other displays to show some aspect of Distortion or Disruption, but what I think you are asking for is something that is absolute, dyed in the wool, no exception Ground Truth. Now some of them are inked prints to inked prints in which 19 other images on the same card exist, plus a photo, plus a signature on a booking sheet and are so close to Ground Truth that you could not slip a chigger in the crack. As for Absolute Ground Truth----they will not fit you bill. They will fit your bill if all you are looking for are examples of distortion (Intra-Source Variation).

Most come from victims, or officers at scenes so they are not disputed that I am aware of. Of the 4,476 latent prints identified in this section so far this year only 9 have been contested in a court of law so far (all nine found guilty). If any interesting comparison was disputed I would not post it out as a FIG.

Can I ask a question-----where did you get the term Intra-Source Variation?

Most recently, from an article I was asked to peer-review for a legal publication. Its in process so I don't feel comfortable saying whose article. I think I've seen it elsewhere, but that could be just a cognitive bias.

I know someone at a presentation is likely to ask about the source of the images, so I wanted to be able to say whether they are known matches (say generated by an examiner for purposes of illustrating the point) or were in dispute, even if the vast majority of examiners would say "yup, that's clearly a match" or "clearly a non-match"

I don't think I have ever heard the term "intra-source." It is quite common to talk about "same source." I am not even sure the meaning would be the same or whether there might be some fine distinction between the two.

Has anyone else ever used or heard the term "intra-source?" Is there any difference between that term and "same source?"

Pat,

Yeah in the community of folks looking at fingerprint statistics, these are commonly used terms. Intra-source variation is essentially represented by the concept of distortion (i.e. "how different can two impressions appear when in fact, they are from the same source skin") versus Inter-source variation (i.e. "how similar can two impressions appear when in fact, they are from different sources)--what we might think of as close non-matches.

In the statistical approaches proposed by Neumann, Champod, Mieuwly, Egli, and others, likelihood ratios represent these two competing parts: intra-source versus inter-source variations. This is intuitive, since analysts are already doing this everytime we offer an opinion. Everytime we report an identification, at some point we weighed the differences observed and asked ourselves, are these differences likely due to a distortion (within tolerance for Intra-source variation) or are they true discrepancies (within tolerance for Inter-source variation)?

So you had experienced these concepts before, but maybe not heard these exact terms.

Also, they differ from Intra-observer variation versus Inter-observer variation. Whereas, the concept in the previous paragraph deals with how the features can present themselves in an impression (what arrangements are possible)...Inter/Intra observer variations deal with how analysts perceive features. What features did I perceive today in an impression versus yesterday or last week (in the same impression) (INTRA-OBSERVER) v. How different are the observation from analyst to analyst all examining the same impression (INTER-OBSERVER). I have some good data on this concept to share with the community soon (in the thesis).

Cheers,

g.

I have seen the term used in the statistical studies completed by the folks involved in AFIS and especially Bio-Metrics. I had just never seen it used in Latent Prints as a substitute for distortion (substituting a 22 character term for a 10 character term is not something most LPE are going to graviate to).

I had a pretty good idea what it meant, I just wanted to be sure that is what Ms Steele was looking for -- Distortion.

A source for the FIGS is at the top and I am sure if you wanted to use one the person that sends them to Kasey would be more than happy to give you the complete source. I think he would like them used for training.

Getting LPE to commit during a presentation, or off a screen, or from a photograph outside their office is going to be difficult. I have tried and that is why I call them interesting comparisons. If I went with a match or non match I would have had so many complaints filed against me with the LPCB that they would have had to buy a new cabinet just for me.

In my PPOV getting the majority of LPE to commit to anything out side their comfort zone is extremeny difficult. Look at this forum. A number of people peruse this site. Less have registered, and fewer still post anything.

Don't count on any LPE jumping up on your presentation and stating "yep that is a match".

g. I cannot wait for the INTER-OBSERVER material. If you have been watching my e-mails off forum site you can realize that I am very interested.

I see it as one of the biggest problems we may have to face in the future. If not for the discipline then for my section at least.

Of course I could be wrong on INTER-OBSERVER material. Looking forward to the material.

I would think 'intra-source variation' is 'within the skin variation' as the volar skin is the source of the impressons. All parts of volar skin varies. The person can be considered the source, the finger can be considered the source, the hand can be considered the source, or the foot can be considered the source. No matter which source is considered, that source skin varies, within itself. The top is different than the bottom and the left side is different than the right. Each ridge has intra-source variation. Split the ridge down the middle and the left side is different than the right, or, intra-ridge variation. Each part of the source is not a mirror image of the opposing side that same source. Bilateral symmetry of specific pattern of features within volar skin does not exist. 'Intra-source variation' is in the skin and should not be the impression. Impressions from the same source vary in appearance.

I would think 'inter-source variation' is variation that occurs 'between or among various skin' or different sources. Different sources will vary, thus impressions from different sources vary.

John V.