Forensic scientists, lawyers and other participants of the legal process are routinely faced with problems of making decisions under circumstances of uncertainty. Uncertainty relates to propositions of interest that are not completely known by the decision-maker at the time when a decision needs to be made. Propositions may relate to the source or nature of forensic traces, marks and objects. For example, with friction ridge marks, propositions of interest may be ‘Does this fingermark come from the person of interest (POI) or from some unknown person?’. In forensic document examination, a scientist may ask ‘Is this a genuine document or has it been modified (e.g., page substitution)?’. In forensic anthropology the question ‘Are these human remains?’ may arise, and so on. Replying in one way or another to such questions may be perceived as uncomfortable since knowledge about the relevant underlying truth-state of the world is incomplete to some extent. For example, in typical real-world applications of forensic science it is not known with certainty, when deciding to consider a POI as the source of a particular fingermark, whether the POI is in fact the source of the fingermark. Similarly, at an advanced stage of the legal process, the question of whether to convict or acquit a POI (i.e. the verdict) needs to be made in the presence of incomplete knowledge about whether or not the POI truly is the offender. There are analogies between the above questions, in terms of their logical underpinnings, that can be studied, analysed and described using formal methods, such as decision theory, which will be the main aim of this chapter. Around the middle of the past century, discussions intensified and several fields of study emerged on decision-making concerning, for example, contexts where decisions have monetary consequences. These developments gravitated around questions such as how decisions should be made in order to be considered rational (Pratt et al., 1964). Though an important area, economics was not the only branch with strong interests in decision-making and decision analysis. Entire fields of study developed and interacted with each other in various ways, including psychology, mathematics and statistics, the law and philosophy of science, among others. This chapter will primarily rely on statistical decision theory1 as developed by Leonard Savage (1954) and in subsequent treatises (e.g., Lindley, 1985; Luce and Raiffa, 1958; Raiffa, 1968) as the framework for studying the formal structure of decision problems arising in forensic science and the law. Before proceeding with this presentation, an important preliminary needs to be considered. It deals with the question of how to understand decision analysis and the notion of theory of decision. To this point, the field of judgment and deci- sion making, a branch of applied psychology, has contributed considerably by crystallizing three main perspectives and approaches, known as the descriptive, the normative and the prescriptive view (Baron, 2008; French et al., 2009). For a review of the history of these terms, see Baron (2006). Broadly speaking, the descriptive approach focuses on peoples’ observable decision behaviour and extends to the development of psychological theories in- tended to explain how individuals make decisions. Such research is valuable in that it allows one to better understand the conditions under which decision behaviour departs towards incoherence or, worse, logical error. However, revealing such departures requires reference points against which observable decision behaviour can be compared. The provision of such reference points, also called normative standards, is the object of study of the normative approach. Decision theory and decision criteria (or, norms) derived from it, fall into this category of study. It is mainly pursued by mathematicians, statisticians and philosophers of science. The third perspective, the prescriptive approach, addresses the question of what recommendations ought to be derived from normative insights in order to improve practical decision making. For example, some strict normativists, such as Lindley (1985), consider that the normative concept of probability – that is, a standard for reasoning under uncertainty – and decision theory as its extension, are also prescriptive in the sense that they provide direct prescriptions on how to arrange one’s reasoning and acting. Properly distinguishing the different intentions and goals of these kinds of decision science research is important for an informed discourse about notions of decision and decision analysis in forensic science applications (Biedermann et al., 2014). This chapter is structured as follows. Section 5.2 outlines standard elements of statistical decision theory that will be exemplified in Section 5.3 for decision problems arising in the law in general (Section 5.3.1) and forensic science in particular (Section 5.3.2). This exposition will include examples such as decisions following forensic inference of source (i.e., identification/individualization; Section 5.3.2.1). Discussion and conclusions will be presented in Section 5.4. Further readings on applications of decision theory in forensic science and treatments of decision theory in general are given in Section 5.5.
Decision theory
Bozza S;
2020-01-01
Abstract
Forensic scientists, lawyers and other participants of the legal process are routinely faced with problems of making decisions under circumstances of uncertainty. Uncertainty relates to propositions of interest that are not completely known by the decision-maker at the time when a decision needs to be made. Propositions may relate to the source or nature of forensic traces, marks and objects. For example, with friction ridge marks, propositions of interest may be ‘Does this fingermark come from the person of interest (POI) or from some unknown person?’. In forensic document examination, a scientist may ask ‘Is this a genuine document or has it been modified (e.g., page substitution)?’. In forensic anthropology the question ‘Are these human remains?’ may arise, and so on. Replying in one way or another to such questions may be perceived as uncomfortable since knowledge about the relevant underlying truth-state of the world is incomplete to some extent. For example, in typical real-world applications of forensic science it is not known with certainty, when deciding to consider a POI as the source of a particular fingermark, whether the POI is in fact the source of the fingermark. Similarly, at an advanced stage of the legal process, the question of whether to convict or acquit a POI (i.e. the verdict) needs to be made in the presence of incomplete knowledge about whether or not the POI truly is the offender. There are analogies between the above questions, in terms of their logical underpinnings, that can be studied, analysed and described using formal methods, such as decision theory, which will be the main aim of this chapter. Around the middle of the past century, discussions intensified and several fields of study emerged on decision-making concerning, for example, contexts where decisions have monetary consequences. These developments gravitated around questions such as how decisions should be made in order to be considered rational (Pratt et al., 1964). Though an important area, economics was not the only branch with strong interests in decision-making and decision analysis. Entire fields of study developed and interacted with each other in various ways, including psychology, mathematics and statistics, the law and philosophy of science, among others. This chapter will primarily rely on statistical decision theory1 as developed by Leonard Savage (1954) and in subsequent treatises (e.g., Lindley, 1985; Luce and Raiffa, 1958; Raiffa, 1968) as the framework for studying the formal structure of decision problems arising in forensic science and the law. Before proceeding with this presentation, an important preliminary needs to be considered. It deals with the question of how to understand decision analysis and the notion of theory of decision. To this point, the field of judgment and deci- sion making, a branch of applied psychology, has contributed considerably by crystallizing three main perspectives and approaches, known as the descriptive, the normative and the prescriptive view (Baron, 2008; French et al., 2009). For a review of the history of these terms, see Baron (2006). Broadly speaking, the descriptive approach focuses on peoples’ observable decision behaviour and extends to the development of psychological theories in- tended to explain how individuals make decisions. Such research is valuable in that it allows one to better understand the conditions under which decision behaviour departs towards incoherence or, worse, logical error. However, revealing such departures requires reference points against which observable decision behaviour can be compared. The provision of such reference points, also called normative standards, is the object of study of the normative approach. Decision theory and decision criteria (or, norms) derived from it, fall into this category of study. It is mainly pursued by mathematicians, statisticians and philosophers of science. The third perspective, the prescriptive approach, addresses the question of what recommendations ought to be derived from normative insights in order to improve practical decision making. For example, some strict normativists, such as Lindley (1985), consider that the normative concept of probability – that is, a standard for reasoning under uncertainty – and decision theory as its extension, are also prescriptive in the sense that they provide direct prescriptions on how to arrange one’s reasoning and acting. Properly distinguishing the different intentions and goals of these kinds of decision science research is important for an informed discourse about notions of decision and decision analysis in forensic science applications (Biedermann et al., 2014). This chapter is structured as follows. Section 5.2 outlines standard elements of statistical decision theory that will be exemplified in Section 5.3 for decision problems arising in the law in general (Section 5.3.1) and forensic science in particular (Section 5.3.2). This exposition will include examples such as decisions following forensic inference of source (i.e., identification/individualization; Section 5.3.2.1). Discussion and conclusions will be presented in Section 5.4. Further readings on applications of decision theory in forensic science and treatments of decision theory in general are given in Section 5.5.File | Dimensione | Formato | |
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