Module 10 - Research Regarding Friction Ridge Impressions

Pattern, incipient ridges, scars, creases

Fingerprint statistical models don’t include _____, _____ _____, _____, or _____.

Minutiae

The easiest data to capture in regard to fingerprint models is related to _____ and aspects of their relationships.

Independent event

The probability of one event does not affect the probability of the other event occurring

Dependent event

An event whose outcome is influenced by the outcome of another event

Dependent

The development of minutiae is a(n) (independent/dependent) event due to the interplay between developmental stability and developmental noise during the embryological development of the ridge arrangements.

Distortion

Impressions of the friction ridge skin bear _____ that can affect the ability to detect minutiae and can alter the properties of a minutia.

1. Ridge structure and description of minutia location

2. Description of minutia distribution

3. Orientation of minutia

4. Variation in minutia type

5. Intra-source variation (distortion)

6. Potential for false match (number of comparisons)

What are Stoney’s six ingredients for a fingerprint model?

Ridge counts, distance

Ridges provide a framework upon which the relative positions of minutia can be compared across ridges (_____ _____) and along ridges (_____).

Recurves and deltas

Local variations in minutiae density depend in part on the presence of what two pattern elements?

1. Ridges are added to the system

2. Ridges are taken away

What are the two fundamentally distinct orientations of minutia (not including dot)?

True

True or False: Orientation is generally robust under mild distortion.

Robust

Ridge counts between minutiae are generally (robust/variable) under ordinary distortion factors.

Variable

Ridge spacing, ridge curvature, and distance and angles between minutiae are (robust/variable) due to the pliability of the skin.

Greater

The more comparisons you perform, the (greater/lesser) the possibility for encountering a chance false match.

Perpendicular, stable

Ridges run (perpendicular/parallel) to growth stresses leading to a developmentally (stable/unstable) pattern.

1. Growth of the hands and feet

2. Regular flexion creases

3. Volar pads

What are the three primary growth stresses during development?

Lengthening

While the hands and feet are growing in all directions, the dominant growth stress is the _____ of the hand or foot.

Ridges run horizontally across most areas of the hands and feet

What is the influence of the dominant growth stress on the ridge flows in the hands and feet?

Ridges circle around the thenar eminence and progress toward the center of the palm

What is the influence of the growth stresses of regular flexion creases on the ridge flows in the hands?

Ridge flows

General paths of groups of ridges that generally reflect the embryological stresses on the surface of the skin caused by the growth of the hands and feet and the formation of the regular flexion creases; distinguished from pattern elements and useful for establishing search parameters

Curvature

The change in angle along a series of parallel ridges at a given location along the ridge flow

Convergence

The loss of ridges along a ridge flow, causing the overall width of the ridge flow to decrease

Divergence

The gain of ridges along a ridge flow, causing the overall width of the ridge flow to increase

Genetics, early

_____ drives the timing of the ridge development. _____ timing typically means the volar pads are more prominent and have more influence on ridge flows.

Volar pads are typically responsible for creating patterns (recurves and deltas)

What is the influence of the volar pads on the ridge flows of the hands and feet?

They are incredibly variable in the population!

Why do whorl ridge counts matter?

Independent

If patterns were _____ events – we could simply multiply their proportions in the population.

Minutia

The end point of a ridge and the primary microscopic landmark within the ridged skin used by examiners, biometric systems, and statistical models

Minutiae density

The number of minutiae per cm²

Minutiae orientation

The direction of the path of the ridge emanating from the minutia

Compound minutia

The combination of multiple minutiae within close proximity or that manifest as a single structure

Pattern force minutiae

Minutiae that tend to form in a predictable density and shared orientation due to their existence in a ridge flow convergence, ridge flow divergence, or proximity to pattern elements (triradii or recurves)

Counter-pattern force minutiae

Minutiae with an orientation opposite the dominant orientation of minutiae in a pattern force region

Unbound minutiae

Minutiae that tend to occur with a less predictable density and orientation due to their existence in a non-pattern force region

Minutiae morphology

Degree of connectedness between the end point of one ridge and a neighboring ridge

Simple

Ending ridges and bifurcations are examples of what type of minutiae?

Compound

Short ridges and dots, enclosures, crossovers, opposing bifurcations, spurs, double bifurcations and trifurcations, and ending ridge and bifurcation combos are examples of what type of minutiae?

Cores and deltas

What are the high-density regions of a fingerprint?

Left, negative

Right loops are dominated by ridges launching _____ from their terminals, or “_____-oriented” minutiae.

Right, positive

Left loops are dominated by ridges launching _____ from their terminals, or “_____-oriented” minutiae.

Flock together

Minutiae tend to “_____ _____,” especially in funneling/pattern force regions. 

Pattern

Minutiae direction depends on _____, and _____ depends on hand/finger.

Right

Right loops are more prevalent on the _____ hand.

Ending ridges

What is the most common type of minutiae?

The perimeter

Where on the fingerprint are ending ridges particularly dominant?

Bifurcations and convergences

What are the second most common minutia types?

Inside

Minutiae are more concentrated (inside/outside) the center of the fingerprint.

Higher

There is a (higher/lower) diversity of minutiae inside the center of the fingerprint.

Thumbs

In the center of the fingerprints, the _____ have the highest number of minutiae and the greatest diversity of minutia types.

Center

Minutiae are more concentrated in the _____ of the fingerprint.

Center

The highest diversity of minutiae occurs in the _____ of the fingerprint.

Enclosures, short ridges

The bottom halves of whorls tend to have a higher frequency of _____ and _____ _____.

Probability of Random Correspondence (PRC)

Statistical model which looks at the probability of randomly selecting a person from the relevant population and finding this same configuration and asks, “What is the probability that a person, other than the subject, randomly selected from the population, will have this configuration of minutia?”

1. Minutiae are uniformly distributed

2. Minutiae are uniform across pattern

3. Minutiae location is an independent event

4. Minutiae direction is an independent event

5. Database size is irrelevant

What are the five untrue assumptions of the PRC statistical model?

Likelihood Ratio

Statistical model that measures the strength of the evidence regarding the hypothesis that the two prints came from the same source and is expressed as a ratio of the probabilities for two hypotheses: 1) this latent was made by this finger and 2) this latent was made by some other finger.

FRStat

Statistical model that calculates a similarity score based on the shapes created by a cluster of minutiae; the final reported number is a ratio based on two distributions based on the number of minutiae: 1) the probability of a false positive at a given score for a given number of minutiae in common and 2) the probability of a false exclusion at a given score for a given number of minutiae in common

A model should be able to distinguish between true matches and close non-matches.

What do we want from a model?

The “gold standard” error rate study by NOBLIS and the FBI in 2011 reported a 0.15% false positive error rate

What is the false positive rate for trained examiners?

Atypical anatomy

Any deviation from the typical range of shape, size, or proportions of the human hand or foot driven by genetic or epigenetic factors

Adolescent growth

Growth of the hand or foot from the time the ridges form until adult size is attained (typically late teens)

Aging

Changes that take place generally after the age of 40

Scar formation

Damage to the hand, foot, or friction ridge skin that elicits a wound healing response

Hand flexion

The bending of the digits at the joints or the rotation of the thumb

Abduction/adduction of the digits

The degree to which the digits are spread apart from each other

Angle of contact

The position of the hand/foot with respect to the surface (e.g., finger parallel to the surface or at a 45-degree angle)

Compressive stress

The squeeze of the skin between the boney portions of the hand or foot and a surface (deposition pressure)

Shearing stress

Tangential force applied to the skin (pushing the skin across a surface – lateral pressure)

Torque

Rotational force applied to the skin

Surface conditions

Any factors related to the surface that affect the recording of the skin (e.g., texture, curvature, pliability, contaminants)

Residue issues

Any factors related to the residue on the skin that can affect the recording of the skin including the following: initial composition of the residue, distribution of residue on the skin, redistribution of residue in an impression due to skin moving on a surface, post-deposition factors, and development technique

Electronic capture errors

Inaccurate recording of a feature by an automated device

The balance of developmental stability and noise

What dictates variation in the population?

1. Humans share some feature sets in common due to the common general form and developmental processes of the hands and feet

2. Impressions from the same source skin inevitably display differences due to distortion factors

3. The examiner’s ability to accurately detect the features

Ease of interpretation of the similarities and differences is influenced by three primary factors: