CLPEX Chat Board

How do you qualify ridge count when using it as a comparative element between a latent and a known?

Being a qualititative element of ridges themselves is this a Level of Detail or a holistic, aggregate attribute of of the impression that falls outside the definition of "detail"?

If someone has an example of a time where they've leaned on the ridge count as a tipping point in an exclusion/individualization, I'd like to hear your thoughts/reasoning behind the conclusion.

thanks,

-Boyd

I cannot see how ridge count can be any more than a nice-to-know part of the analysis even before comparison. If the unknown latent is of such quality and quantity that a ridge count (delta to core?) can be performed, I would submit that it is still only one of a few features of detail used in comparison when attempting to individualize a latent.

When we worked with single fingers in the early 90's, it was always a subject of warm to hot debate as deltas and cores can sometimes be open to subjective personal observation and interpretation. Further, what I would see as a 10 ridge count, could be seen by a colleague as 9 or 11.

For this reason I would give no more individualization consideration to ridge count than I would give to pattern type.

I vote for holistic attribute.

antonroland wrote:... I would submit that it is still only one of a few features of detail used in comparison when attempting to individualize a latent.

For this reason I would give no more individualization consideration to ridge count than I would give to pattern type.

I vote for holistic attribute.

What about for the purpose of exclusion?

You know, I think we have to describe all comparison as ultimately holistic. Or rather, it's an alternating sequence of holistic and discrete. To clarify, let me line out how I present crime scene investigation when I teach. The first approach is holistic, an overall survey to gain a general impression and to determine the physical scope of the field we will examine as the scene. We then deal with individual features of the scene as discrete objects. We don't know enough yet to relate them to each other. When we have done all we do with individual objects, we return to a holistic mode to identify relationships and meaning. I consider it important that the class understands the concept of orientation, addressing individual objects without preconception or limitation, and then complete openness to critical comparison of the whole to the events that produced them. This means I would characterize crime scene investigation as fundamentally holistic, with discrete treatment of details necessary to avoid distortion.

In the above example, different objects will have different weights on account of differences in clarity, potential, and inherent characteristics. Isn't latent examination like that? Features weight first by clarity. A set of generally low quality features may have little power to individualize but may exclude. Features that can be clearly identified as a particular named detail type have high potential as evidence of individualization or exclusion, depending, of course, on relationships. It is a characteristic of plain ridges, that no matter how clearly impressed, they have little weight in individualization but may, in conjunction with other features exclude. Like crime scene work, the discrete stage of addressing individual objects is entirely concerned with the best possible representation of that object and not at all with its meaning. When I look at a latent feature, my only concern is to determine if it can be clearly described and what sort of skin feature it represents. And there is another important analogue with the crime scene. In crime scene work, I generally cannot go back in the analysis stage and recover something I should have dealt with on the scene but didn't. Sometimes I can, but there is a danger of corruption, a reduction in weight and confidence. In latent examination, this is analogous to being driven to more closely examine a feature because I "need" it in analysis, and that's dangerous.

The discrete decisions in latent print examination, the determination of identity and weight of features, is strictly objective. (We had this discussion a while back, and I don't want to restart that thread. If you have a problem with this being objective, read that thread for various interpretations.) We will identify the feature with certainty, in which case, we will assign it considerable weight and potential, or we will, with certainty, determine it cannot be certainly identified. Everything we can observe in a latent will have any combination of weight and potential, depending on what we know of that sort of thing. Ridge count has one combination. Ridge flow has another. A ridge detail like a bifurcation has another. In the analysis stage, the physical relationships among features realize or fail to realize the potential, to one degree or another. A clear core and delta and intervening ridges may become a very powerful excluder, even when other features display matching relationships with the record. Even an approximate count may have this power.

We can't get so bound up in discriminating among Level I, II, and III detail that we lose our orientation to how we really use everything in the impression. The observation made on ridge count is discrete, as are all observations. It operates in analysis as holistic, as is all analysis.

Ridge count has two distinct aspects as applied to fingerprint matching. One is in determining the “size” of the fingerprint and is usually applied in classification formulae. The other is when we try to establish a correlation between Galton points or acknowledge a lack thereof.

Obviously, the “size” of a print can be used to exclude a potential source. Placement of deltas and cores is not an issue since the examiner will place these in the same relative position on the known and questioned prints. What other examiners do is irrelevant (unless you’re trying to do a telephone evaluation of potential suspects). But the examiner is cautioned: “double taps,” scarring and other distorting influences can affect the appearance of the print and lead to error.

Ridge count as it relates to “size” is a level 1 feature because it has limited value to individualize. I’m sure there are millions, if not billions, of 10 count right slant loops out there.

Ridge count as it relates to the correlation between Galton points is part of the level 2 evaluation of the print. Level 2 can not individualize if there is no ridge count correlation between points.

Consideration of all three levels of ridge detail is the holistic approach, so any one level is part of the whole process.

Steve Everist wrote:

antonroland wrote:... I would submit that it is still only one of a few features of detail used in comparison when attempting to individualize a latent.

For this reason I would give no more individualization consideration to ridge count than I would give to pattern type.

I vote for holistic attribute.

What about for the purpose of exclusion?

May I use the old cliche of "show me the print"?

If ridge count is clearly discernible in both latent and known, then surely, there should be some value in the purpose of exclusion if the ridge count is clearly off the mark.

But what if the ridge count is close or identical?

Surely then we will have to revert to other detail visible in the latent.

Whether near, identical or way off I am sure we will all agree that neither individualization nor exclusion can ever happen on only ridge count only.

antonroland wrote:

Steve Everist wrote:

antonroland wrote:... I would submit that it is still only one of a few features of detail used in comparison when attempting to individualize a latent.

For this reason I would give no more individualization consideration to ridge count than I would give to pattern type.

I vote for holistic attribute.

What about for the purpose of exclusion?

May I use the old cliche of "show me the print"?

If ridge count is clearly discernible in both latent and known, then surely, there should be some value in the purpose of exclusion if the ridge count is clearly off the mark.

That's my point. So often we focus on the purpose of individualization whereas the large majority of the results of our comparisons are exclusions. After analysis, if the latent is determined to be of a quality that the pattern type and ridge count aren't in question, and the ridge count is in the 20's while the known exemplar available has no ridge counts that reach 10 - how much further do you feel it is necessary to go?

The first part of the original question asks about how ridge count is qualified as a comparative element. If there's a drastic difference between two ridge counts when the latent and known are of the same pattern, and have gone through a thorough analysis, then using ridge count could be enough to tip towards exclusion. In this respect it qualifies similar to Level 1 exclusions when the quality and quantity are high. But when quality and quantity are low, it may not be enough to render a conclusion. Yet it's never enough to be able to individualize.

But what if the ridge count is close or identical?

Surely then we will have to revert to other detail visible in the latent.

Exactly - in those situations it doesn't qualify to be enough to exclude. This also goes for poor quality and quantity where there may be some question as to the ridge count's accuracy. In these situations, the amount needed to render a conclusion is going to have to include more than a ridge count (or pattern type) for exclusion and the amount needed for individualization is going to be higher than it would if the clarity were better.

Whether near, identical or way off I am sure we will all agree that neither individualization nor exclusion can ever happen on only ridge count only.

I guess my answer to that will be in the form of a question - do you think that exclusion can ever happen at pattern type only?

Steve

Sorry I dropped the ball here a LOOOONG while back and only happened to notice this thread now whilst looking for something else - please forgive me.

If your last post wanted an answer rather than it being purely rhetorical I will submit the following...

Exclusions purely on pattern could be a safe way to do it maybe 70-80% of the time. That said, how do we define pattern based exclusions? How much will we allow for distortion?

I think you will agree that we are in murky water here simply because at some stage I would like to believe one would necessarily start looking at minutiae and other features and by then it is already no longer an exclusion based on pattern only...

Coming back to holistic then any way we look at it...

Anton

PS, forgive me if I stated the obvious