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The purpose of this chapter has not been to advance any argument or to develop theoretical propositions. Rather, its objective has been the much more mundane one answering to the motivations set out in §3.1: laying out basic factual information concerning the practice of FSC internationally in the present day and drawing upon the collective expertise of FSC experts worldwide so as to identify current working methods and features of speech that are considered to have the greatest potential for discriminating between individuals.

Those not directly involved in this specialist field but working, for example, in other aspects of phonetics or linguistics, may well be surprised at the lack of consensus over such fundamental matters as how speech samples are to be analyzed and compared, which aspects of the samples are to be assigned greatest importance during the analytic process, and how conclusions are to be expressed at the end of it. However, we are assured by those working in various other fields of forensic science that the level of dissensus uncovered by the present survey is by no means unique to forensic speaker comparison. Indeed, some of the practices and preferences found here are undoubtedly dictated or constrained by the rules of the institutions and firms in which the participants work. Where those organizations include other forensic science disciplines, the options, particularly for the framing of conclusions, may be laid down unilaterally for all types of casework investigation undertaken under their auspices. For instance, the Dutch government forensic science facility, the Netherlands Forensic Institute, requires that the outcomes of every investigation undertaken by its employees, irrespective of the forensic discipline, be expressed within a Bayesian likelihood ratio framework (Meuwly,

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p. c.). Likewise, one of the participants in the present study who used a binary decision format when expressing conclusions stated that to do so was a requirement of his/her employer.

Over and above the rules laid down by public and private sector laboratories, nations may also set down requirements, either by statute or via case law. Some jurisdictions, notably the England and Wales division of the UK, have been extremely non-prescriptive in this respect, according the expert a very high degree of autonomy and discretion over the methods of analysis he/she adopts and the way the outcomes are formulated. In respect of forensic speaker comparison evidence, the England and Wales position was affirmed in the Appeal Court ruling R -v- Robb (1991), in which the court ruled that whether or not an expert used any acoustic testing was entirely his/her own decision, and re-iterated in relation to the same issue in the more recent appeal R -v- Flynn and St John (2008). Indeed, the main analytic issues over which the higher courts have seen fit to pass down general prohibitions to forensic experts concern the use of statistics in representing the strength of evidence (cf. R -v- Doheny and Adams (1996); R -v- T (2011)). Where experts enjoy freedom of choice, one might expect their preferences to be influenced by individual intellectual commitments. However, in spite of the latitude allowed by the UK legal system, it is of note that all nine UK experts taking part in the study use the combined AuPA + AcPA method. Indeed, this method is the predominant one across all countries represented in the survey (25 = AuPA + AcPA; 10 = other – see Table 3.3). Thus, although the results show a wide range of variation in methods, there is nevertheless a very large degree of convergence.

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As for the future, certain trends can be predicted. One is that as time goes on and further improvements are made to the error rates of (semi)automatic systems and to their capabilities for handling real case (i.e., non-studio) recordings, one would expect to find such systems increasingly being incorporated into casework alongside the AuPA + AcPA approach. This development would be particularly apposite in the USA, where the appeal court ruling Daubert -v- Merrell Dow Pharmaceuticals Inc. (1993) is taken by many lower courts as the benchmark for admissibility of expert evidence, and within that ruling is the statement that ‘the court ordinarily should consider the known or potential error rate’ of the method. ASRs readily lend themselves to meeting this criterion, and, indeed, many systems are subject to such testing as part of the annual NIST evaluations (Greenberg et al., 2010). Further, a number of ASRs have an LR as one of their easily selectable options for representing the results of speaker comparisons. As seen in Table 3.3, most experts currently express their conclusions in terms of a classical probability scale (14), whilst only half as many (7) use some form of LR (3 = verbal LR; 4 = numerical LR). The increasing use of ASR software, together with the current ‘paradigm shift’ in forensic science towards Bayesian reasoning, and the use of LRs for presenting results, would lead one to expect an increase in the number of experts using LRs and a corresponding decrease in the use of other conclusion frameworks.

Morrison (2009c, p. 298) suggests that today we are in the midst of what Saks and Koehler (2005) have called a paradigm shift in the evaluation and presentation of evidence in the forensic sciences which deal with the comparison of the quantifiable properties of objects of known and questioned

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origin, e.g., DNA profiles, finger marks, hairs, fibres, glass fragments, tool marks, handwriting and voice recordings.” However he fails to acknowledge the fact that not all speech evidence is of the quantifiable type, as demonstrated in the survey results from the present study. The Bayesian framework of likelihood ratios has been adopted by many fields in the forensic disciplines where quantifiable evidence is of the norm and qualitative evidence is something that does not necessarily come into question (e.g. DNA or fingerprints). It is important to recognize that speech does not consist entirely of measurements. There are elements of speech that are best described/analyzed qualitatively (i.e. certain aspects of voice quality (e.g. lingual body orientation), lexical, syntactic, or morphological choices, audible breathing, laughter). If such features can be quantified in some form, then it is plausible that we will one day see an entire forensic speaker comparison case completed in a Bayesian framework, but until then there will still be experts who will continue to present such features in a qualitative form, whether that is alongside a LR conclusion or another form of conclusion (e.g. CPS or UK Position Statement).

Additionally, in light of the popularity of the Bayesian framework, it can be predicted that more research on LRs will be carried out. This can be seen as a positive trend, as parameters that experts found to be discriminant in their experience (as reported in this survey), may now be tested empirically, and general strength of evidence statements can potentially be attributed to certain features. Given this, experts and researchers in the field of forensic speech science can give appropriate weight in forensic casework to those features

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found to be most discriminant through intrinsic14 _{and extrinsic}15 _likelihood ratio testing.

Finally, those differences that currently exist across practitioners may be reduced through blueprints16 _{and drives for international co-operation and} cross-border transferability of forensic science evidence (e.g. House of Commons Northern Ireland Affairs Committee, 2009). And, of course, the prerequisite for resolution of differences is knowledge of their existence. Insofar as the present study lays bare that information, it may be considered to be making a modest first step towards international unity.