The T-Model defines the total value of a ridge feature during the analysis phase a latent and or exemplar fingerprint impression as the product of its quantity (shape and position) and quality (clarity and reliability).  Qualitative metrics were designed to reflect reduced levels of ridge feature quality in terms of reduced visual clarity and reduced reliability.  Reduction factors were designed to reduce the quantitative weight in proportion to reduced levels of ridge unit clarity and reliability, keeping in mind the need for optimum reproducibility, simplicity, and sensitivity. 

A 5-tier qualitative grading scale (e.g., A, B, C, D, F) with corresponding reduction factors (e.g., 1.00, 0.75, 0.50, 0.25, 1/P), was designed based on objective criteria as follows:

Ridge Feature Clarity / Reliability Grade Scale – ANALYSIS

No Distortion  (Grade A - Reduction Factor = 1.00 )

Criteria:  Ridge feature appears visually clear and reliable, e.g., consistent with normal ridge structure.

Weak or Low Distortion (Grade B - Reduction Factor = 0.75)

Criteria:  Ridge feature appears visually unclear (1) or unreliable (2), and within tolerance to include (3).

Moderate Distortion (Grade C - Reduction Factor = 0.50)

Criteria:  Ridge feature appears visually unclear and unreliable, and within tolerance to include.

Strong or High Distortion (Grade D - Reduction Factor = 0.25)

Criteria:  Ridge feature appears obstructed however the orientation and relative position are reliably predictable.

Extreme Distortion (Grade F - Reduction Factor = 1/P (4))

Criteria:  Ridge feature appears too distorted to analyze.

(1) The term "unclear" refers to ridge features that may be obstructed, cloudy, faint, and so on.

(2) The term "unreliable" refers to ridge features that may be inconsistent with normal ridge structure, contain distortion markers, red flags, and so on. 

(3) The phrase "within tolerance to include" refers to interpretations and assessments that are grounded in experimentation, e.g., friction ridge skin elasticity experiments, ridge feature distortion experiments, and so on, and professional judgment.

(4) 1/P denotes neutralization of ridge feature weight, e.g. a ridge feature quantitative-qualitative value of 1.

Click here to view PDF version of above qualitative table in Quick Start instructions of the T-Model Fingerprint Calculator.

It is significant to note that the quantitative interpretation of ridge feature types (and their subsequent weight) and the qualitative assessment of ridge feature clarity and reliability (and their subsequent reduction factor, if any), are based on the professional judgment of the latent print examiner trained to competency, which means the successful passage of training exercises and a formal examination involving the above qualitative map.  

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For purposes of increased ability to reliably reproduce previous results, reduction factors are equally distributed by factors of .25 (e.g., based on reduced levels of ridge feature clarity and/or reliability).

Although exemplar ridge units generally display strong ridge unit clarity and reliability, the same qualitative assessment should be applied in the event either diminished clarity and/or reliability is observed.  For purposes of conservativeness, ambiguous ridge detail clarity or reliability should be subject to reduction and default to lower bound values.