SSSS I-9/2013 RGEP.1258 SSSS
5.2 P REGUNTAS DE R ESPUESTA O RAL
5.2.1 P REGUNTAS DE R ESPUESTA O RAL EN P LENO
4.4.3.1. Objective 4.3.1. Analysis of fingerprint examiner usability decision rationale
The decision rationale of 4 fingerprint examiners provided in relation to 30 fingerprint usability determinations were analysed. These usability determinations were made with access to good quality tenprint sets of the same source as the experimental images (as detailed in the Method, section 4.3), thus allowing the examiner the best possible chance to make an identification. During this process examiners were asked to make usability decisions through the process of identification and to provide their reasons for their decisions. Rationale were analysed through taking the same Ground Theory type approach as taken in relation to practitioner data (see section 4.3).Grounded theory style analysis resulted in the identification of a total of 35 decision factors. These decision factors were grouped according to six decision categories. These were:
Clarity/movement Pattern/1st level detail
2nd level detail
Area of mark present
Sequential ridge count and continuity or ridges Would get second opinion
Page | 147 The factors and frequency of factors making up each decision category are provided in Table 4.3. A description of decision factors for each decision category is provided below.
Clarity/movement
Decision factors within the ‘clarity/movement’ category cover aspects of the general clarity of the mark, such as ‘faint’, ‘dotty’, or ‘blurry’, and also factors which relate to movement or superimposition in the mark, for example ‘movement in mark’ or ‘superimposed’. Movement in mark is the most commonly reported rationale within this category. Clarity in ridges is also stated on a number of occasions. This category contained the largest number of decision factors (13).
Pattern/1
stlevel detail
Only four factors were recorded within this decision category and there was a low representation of all of these factors. These involved the presence or absence of either a core or pattern within the fingermark.
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2
ndlevel detail
The second level detail category was the second largest represented in terms of number of decision factors (with 10 decision factors). Key decision factors within this category were ‘sufficient detail’ (mentioned on 25 occasions), ‘insufficient detail’ (mentioned on 28 occasions) or reference to a ‘numerical value of characteristics (26 occasions). An interesting factor within this category is ‘points in agreement’ which is referring to a comparative approach to quality assessment (i.e. there are points in agreement between the experimental fingermark and the set of tenprint images provided), and is a clear difference in approach to quality assessment to that of laboratory practitioners.
Area of mark present
Only one decision factor was assigned to this category. Examiners stated that the ‘area of the mark present’ had affected their decision making on six occasions.
Sequential ridge count and continuity of ridges
This category collates factors related to identifying the presence or absence of sequential ridges within a fingermark and the sequential counting of characteristics. Six factors are included within this category. The inclusion of factors such as ‘characteristics in coincident sequence’ highlight the importance of continuity in the examiner decision process which was not so prominent within the practitioner quality assessment rationale.
Would get second opinion
The decision factor ‘would get second opinion’ was given as a decision rationale on two occasions. This is similar to practitioner factors such as ‘would get a peer’s opinion’ as included within the practitioner ‘Unsure’ decision category.
The total number of factors reported by examiners within each of the six decision categories are compared within Figure 4.12. This illustrates that ‘2nd level detail’ was the most reported decision
rationale by the examiners (on 96 occasions), and that ‘clarity/movement’ was also frequently reported (on 89 occasions). ‘Pattern and 1st level’ detail factors were reported considerably less often
Page | 149 Figure 4.12 - Occurrence of decision factors within each decision category for examiner usability decisions
4.4.3.2. Objective 4.3.2. A comparison of decision rationale between practitioners and
examiners
Practitioner decision rationale from both laboratories (Lab A and the MPS Laboratory) in relation to the same 30 experimental fingermarks examined with reference to examiner decision making in Objective 4.3.1 was collated. ‘No response’ factors were removed from this data set in order to allow a comparison of only decision related factors. The proportionate make-up of decision categories for the practitioner group and the examiner group are presented in Figure 4.13.
Due to the nature of the Ground Theory style analysis there are slight differences in decision categories between the two groups. However, the categories of ‘clarity’, ‘1st level detail’, ‘2nd level
detail’ and ‘area of mark’ are present in both data sets and so can be compared. Both the practitioner and examiner groups can be seen to exhibit the same (and largest) percentage of rationale in relation to ‘2nd level detail’ (43%). Within the practitioner group there is a similar proportion of ‘clarity’ (25%)
and ‘1st level detail’ (22%) decision categories. In the examiner group, however, ‘clarity’ makes up a large proportion of decision categories (41%), whilst ‘1st level detail’ accounts for a small proportion
(5%). 89 9 96 6 16 2 0 10 20 30 40 50 60 70 80 90 100 Clarity/movement
Pattern/1st level detail 2nd level detail Area of mark present Sequential ridge count and continuity of ridges Would get second opinion
OCCURENCE OF DECISION FACTORS WITHIN CATEGORY
DE C ISI ON C A T E G OR Y
Occurrence of decision factors within each
decision category for examiner usability
Page | 150 Figure 4.13 - A comparison of the make-up of decision rationale categories between practitioners and examiners
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4.5.
Summary of key findings
The key findings of empirical research within this chapter are summarised as follows:
Objective 4.1. To explore the rationale behind laboratory practitioner fingermark submission
decision making within Laboratory A.
Objective 4.1.1. A qualitative assessment of practitioner self-reported submission decision
rationale within Laboratory A
A broad range of rationale were reported by practitioners when deciding whether to submit or discard an experimental mark.
Most commonly reported categories of rationale were associated with 2nd level detail and
clarity of the mark.
Within the category of ‘2nd level detail’, factors which indicated that a count or threshold of
minutiae was important made up a total of 78% of responses.
Objective 4.1.2. An assessment of inter-practitioner variation in fingermark submission
decision rationale with Laboratory A
The make-up of decision categories across individual practitioners was largely representative of the overall make-up of decision categories.
There were some individual differences in the type of decision rationale reported. There were individual differences in the number of rationale reported.
The ‘no response’ decision factor was more common amongst the responses of a minority of participants.
Objective 4.1.3. An assessment of practitioner fingermark submission decision rationale
according to experimental fingermark
There are similarities in the proportion of self-reported decision categories according to experimental mark.
Objective 4.2. An investigation of inter-laboratory consistency in practitioner decision rationale
There were overall similarities in the decision categories observed across the twometropolitan UK police force laboratories.
The was a difference in the relative proportion of the ‘clarity’ and ‘1st level detail’ decision categories between the two laboratories, with the MPS laboratory reporting more decision
Page | 152 factors within the ‘1st level detail’ category, than the ‘clarity’ category, and the reverse being
true of Laboratory A.
There were overall similarities in the make-up of decision categories given for both categories of crime by both laboratories.
In the case of the MPS Laboratory there was a decrease in the proportion of the ‘2nd level
detail’ and the ‘clarity’ categories and an increase in the proportion of ‘no response’ responses from the serious to the volume crime category.
Objective 4.3. Exploring the relationship between practitioner submission decision rationale
and fingerprint examiner usability rationale
Objective 4.3.1. An assessment of fingerprint examiner self-reported usability decision making
rationale
Fingerprint examiners reported a range of rationale for fingermark usability decision making. Decision factors reported were most commonly related to the use of ‘2nd level detail’, whilst
‘clarity’ and ‘movement in the mark’ was also a key category of rationale.
Objective 4.3.2. A comparison of fingermark practitioner submission decision rationale and
fingerprint examiner usability decision rationale
There were overall similarities in the categories of decision rationale stated by examiners and practitioners.
There was, however, a difference between the proportion of responses in relation to 1st level
detail and the clarity of a fingermark, with examiners relying more heavily on factors relating to mark clarity and practitioners relying more heavily on factors associated with the presence of pattern or 1st level detail and focusing upon continuity within a fingermark.