Page 193 - Automated Fingerprint Identification Systems (AFIS)

178 AUTOMATED FINGERPRINT IDENTIFICATION SYSTEMS

Figure 8.3
Remaining
Prints Remaining After latent prints
Elimination Prints examined in
HQ
Agency A Agency B

Of 60 prints, Of value Of 100 prints,
50 are “of value” determination 70 are “of value”
5 cases 7 cases

60 lifts examined at headquarters 100 lifts examined at headquarters
10 have no value 30 have no value
50 lifts remain 70 lifts remain

Time for a statistical recap. Both agencies went to ten crime scenes and
looked at 100 latent images. Agency A considered 20 from two crime scenes to
be of no value and did not process them any further. The number of latent
images retrieved from the eight remaining crime scenes is 80. This is the base
for any further comparisons. Agency B did not make any quality determination
at the ten crime scenes and retained all 100 latent images. Their base for further
comparisons is 100 latents from ten crime scenes. Agency A has 20% fewer
latent images to search than Agency B, and their images are of reasonably good
quality. The quality of each of the 100 images for Agency B is unknown. The
denominator for Agency A is 80, and the denominator for Agency B is 100.
With the use of the elimination print process, however, Agency A reduced this
denominator to 60. Agency A could also claim a 25% identification rate (20
elimination prints identified from the group of 80, i.e., 20 divided by 80).
Agency B has an identification rate of 0%.
Back at headquarters, both teams used photographic technology for a better
view of the latent images. The technicians from Agency A removed an addi-
tional ten images that were of no value. The Agency B technicians removed 30
images that were not of value. The denominator of Agency A is now 50, and
the denominator of Agency B is now 70.
Next, Agency A searches the remaining 50 latent images on the AFIS systems,
while Agency B searches their 70 prints. As shown in Figure 8.4, each agency
makes 25 identifications that close three cases.
What is the resulting ident or hit rate for each agency? There is no simple
answer. The hit rate for Agency A may be

• 56% of latents (20 elimination print idents plus 25 AFIS idents from 80 latent
images)
• 62% of cases (45 idents in five of the eight cases)