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Nordgaard, Anders
Publications (10 of 39) Show all publications
Nordgaard, A. (2016). Editorial Material: Comment on Dismissal of the illusion of uncertainty on the assessment of a likelihood ratio by Taroni F., Bozza S., Biederman A. and Aitken C.(1) in LAW PROBABILITY and RISK, vol 15, issue 1, pp 17-22. Law, Probability and Risk, 15(1), 17-22
Open this publication in new window or tab >>Editorial Material: Comment on Dismissal of the illusion of uncertainty on the assessment of a likelihood ratio by Taroni F., Bozza S., Biederman A. and Aitken C.(1) in LAW PROBABILITY and RISK, vol 15, issue 1, pp 17-22
2016 (English)In: Law, Probability and Risk, ISSN 1470-8396, E-ISSN 1470-840X, Vol. 15, no 1, p. 17-22Article in journal (Other academic) Published
Abstract [en]

n/a

Place, publisher, year, edition, pages
OXFORD UNIV PRESS, 2016
National Category
Mathematics
Identifiers
urn:nbn:se:liu:diva-127579 (URN)10.1093/lpr/mgv006 (DOI)000373577400002 ()
Available from: 2016-05-03 Created: 2016-05-03 Last updated: 2017-11-30
Ahlinder, J., Nordgaard, A. & Wiklund Lindström, S. (2015). Chemometrics comes to court: evidence evaluation of chem–bio threat agent attacks. Journal of Chemometrics, 29(5), 267-276
Open this publication in new window or tab >>Chemometrics comes to court: evidence evaluation of chem–bio threat agent attacks
2015 (English)In: Journal of Chemometrics, ISSN 0886-9383, E-ISSN 1099-128X, Vol. 29, no 5, p. 267-276Article in journal (Refereed) Published
Abstract [en]

Forensic statistics is a well-established scientific field whose purpose is to statistically analyze evidence in order to support legal decisions. It traditionally relies on methods that assume small numbers of independent variables and multiple samples. Unfortunately, such methods are less applicable when dealing with highly correlated multivariate data sets such as those generated by emerging high throughput analytical technologies. Chemometrics is a field that has a wealth of methods for the analysis of such complex data sets, so it would be desirable to combine the two fields in order to identify best practices for forensic statistics in the future. This paper provides a brief introduction to forensic statistics and describes how chemometrics could be integrated with its established methods to improve the evaluation of evidence in court.

The paper describes how statistics and chemometrics can be integrated, by analyzing a previous know forensic data set composed of bacterial communities from fingerprints. The presented strategy can be applied in cases where chemical and biological threat agents have been illegally disposed.

Place, publisher, year, edition, pages
John Wiley & Sons, 2015
Keyword
evidence evaluation, likelihood ratio, forensics, chemometrics, Bayes factor, correlated variables
National Category
Analytical Chemistry Bioinformatics and Systems Biology Probability Theory and Statistics Law and Society
Identifiers
urn:nbn:se:liu:diva-118566 (URN)10.1002/cem.2699 (DOI)000355229400001 ()
Funder
Swedish Civil Contingencies Agency
Available from: 2015-06-01 Created: 2015-06-01 Last updated: 2018-03-09
Sydsjö, G., Kvist, U., Bladh, M. & Nordgaard, A. (2015). The optimal number of offspring per gamete donor. Acta Obstetricia et Gynecologica Scandinavica, 94(9), 1022-1026
Open this publication in new window or tab >>The optimal number of offspring per gamete donor
2015 (English)In: Acta Obstetricia et Gynecologica Scandinavica, ISSN 0001-6349, E-ISSN 1600-0412, Vol. 94, no 9, p. 1022-1026Article in journal (Refereed) Published
Abstract [en]

Our aim was to create a mathematical basis to calculate the risks for unintended matings of consanguineous half-siblings from a donor in a society with approximately 10 million inhabitants. The Curie-Cohen model for calculation of the risk for consanguineous mating was used. When the number of offspring per donor is limited to 10, then the model gives a yearly risk for consanguineous matings below 1%. Thus 10 offspring gives a risk for consanguineous matings of 0.9% per year, or approximately once in every 100years. The risk increases exponentially: with 15 offspring it exceeds 2% and with 25 it reaches up above 5%.

Place, publisher, year, edition, pages
Informa Healthcare / Wiley, 2015
Keyword
Number of children; donor; mathematical model; consanguinity; fertility
National Category
Clinical Medicine Mathematics
Identifiers
urn:nbn:se:liu:diva-120855 (URN)10.1111/aogs.12678 (DOI)000359086600017 ()26014908 (PubMedID)
Note

Funding Agencies|National Tissue Group for Gametes (VOG Konsceller) at the National Council for Human Organs and Tissues (Nationella Vavnadsradet) at the Swedish Association of Local Authorities and Regions (SALAR)

Available from: 2015-08-28 Created: 2015-08-28 Last updated: 2017-12-04
Nordgaard, A., Emanuelson, A., Mannerskog, S., Svensson, U., Ekberg, K., Jonasson, L., . . . Leitet, E. (2014). Indirect Evaluation by Simulation of a Bayesian Network. In: : . Paper presented at 9th International Conference on Forensic Inference and Statistics (ICFIS2014).
Open this publication in new window or tab >>Indirect Evaluation by Simulation of a Bayesian Network
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2014 (English)Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

Evidence evaluation when addressing source level propositions is usually done by comparing a piece of recovered material from (specimens of) control material. When the control material source is not available for taking specimens or for investigating it in its entirety, we must stick to photographs or video take-ups for making comparisons. An example is the comparison of class characteristics between a recovered footwear print and a picture of a seized shoe, where the evaluation is occasionally made that way. However, this way of pursuing the investigation is due to needs of quick answers, when there is no or little time to send in the entire footwear for the comparison. Moreover, the pictures taken of the sole of the seized footwear are taken by the police under controlled conditions and with high quality equipment.

When the suspected source is captured on a lower quality video take-up and the recovered material consists of fragments from the original body of material – for instance fire debris – the comparison with the control material source is naturally more difficult. In this paper we present a case where the question is whether recovered fire debris originate from a piece of garment captured on a CCTV take-up. We show how a likelihood ratio for the two propositions can be indirectly obtained from a classification of the source of the fire debris, by using a Bayesian network model. Results from fire debris analysis as well as the results from image comparisons can be evaluated against propositions of class and the updating of the class node for fire debris propagates back to the propositions for source.

Feeding the network with uniform priors for the class nodes we show how simulation can be used to obtain the correct level of the likelihood ratio for further reporting.

Keyword
Bayesian networks, trace evidence, digital evidence
National Category
Probability Theory and Statistics Law and Society
Identifiers
urn:nbn:se:liu:diva-118548 (URN)
Conference
9th International Conference on Forensic Inference and Statistics (ICFIS2014)
Available from: 2015-06-01 Created: 2015-06-01 Last updated: 2015-06-01
Ansell, R., Nordgaard, A. & Hedell, R. (2014). Interpretation of DNA Evidence: Implications of Thresholds Used in the Forensic Laboratory. In: : . Paper presented at 9th International Conference on Forensic Inference and Statistics (ICFIS2014).
Open this publication in new window or tab >>Interpretation of DNA Evidence: Implications of Thresholds Used in the Forensic Laboratory
2014 (English)Conference paper, Poster (with or without abstract) (Other academic)
Abstract [en]

Evaluation of forensic evidence is a process lined with decisions and balancing, not infrequently with a substantial deal of subjectivity. Already at the crime scene a lot of decisions have to be made about search strategies, the amount of evidence and traces recovered, later prioritised and sent further to the forensic laboratory etc. Within the laboratory there must be several criteria (often in terms of numbers) on how much and what parts of the material should be analysed. In addition there is often a restricted timeframe for delivery of a statement to the commissioner, which in reality might influence on the work done. The path of DNA evidence from the recovery of a trace at the crime scene to the interpretation and evaluation made in court involves several decisions based on cut-offs of different kinds. These include quality assurance thresholds like limits of detection and quantitation, but also less strictly defined thresholds like upper limits on prevalence of alleles not observed in DNA databases. In a verbal scale of conclusions there are lower limits on likelihood ratios for DNA evidence above which the evidence can be said to strongly support, very strongly support, etc. a proposition about the source of the evidence. Such thresholds may be arbitrarily chosen or based on logical reasoning with probabilities. However, likelihood ratios for DNA evidence depend strongly on the population of potential donors, and this may not be understood among the end-users of such a verbal scale. Even apparently strong DNA evidence against a suspect may be reported on each side of a threshold in the scale depending on whether a close relative is part of the donor population or not. In this presentation we review the use of thresholds and cut-offs in DNA analysis and interpretation and investigate the sensitivity of the final evaluation to how such rules are defined. In particular we show what are the effects of cut-offs when multiple propositions about alternative sources of a trace cannot be avoided, e.g. when there are close relatives to the suspect with high propensities to have left the trace. Moreover, we discuss the possibility of including costs (in terms of time or money) for a decision-theoretic approach in which expected values of information could be analysed.

Keyword
DNA, traces recovery, extraction, typing
National Category
Biochemistry and Molecular Biology Probability Theory and Statistics Law and Society
Identifiers
urn:nbn:se:liu:diva-118546 (URN)
Conference
9th International Conference on Forensic Inference and Statistics (ICFIS2014)
Available from: 2015-06-01 Created: 2015-06-01 Last updated: 2015-06-10
Nordgaard, A. (2014). Interpreting findings – evaluation and conclusions about what happened at the crime scene. In: : . Paper presented at Annual meeting of ENFSI Scene of Crime Working Group.
Open this publication in new window or tab >>Interpreting findings – evaluation and conclusions about what happened at the crime scene
2014 (English)Conference paper, Oral presentation only (Other (popular science, discussion, etc.))
Keyword
crime scene investigation, knowledge building, evaluative expressions
National Category
Law and Society Probability Theory and Statistics
Identifiers
urn:nbn:se:liu:diva-118550 (URN)
Conference
Annual meeting of ENFSI Scene of Crime Working Group
Available from: 2015-06-01 Created: 2015-06-01 Last updated: 2015-06-01
Nordgaard, A., Andersson, K. & Högberg, C. (2014). The Multivariate Kernel Likelihood Ratio Method Applied on Comparison of Amphetamine Seizures. In: : . Paper presented at 9th International Conference on Forensic Inference and Statistics (ICFIS2014).
Open this publication in new window or tab >>The Multivariate Kernel Likelihood Ratio Method Applied on Comparison of Amphetamine Seizures
2014 (English)Conference paper, Oral presentation with published abstract (Other academic)
Abstract [en]

Comparison of seizures of amphetamine with respect to their origins of illicit manufacturing can be done by investigating the amphetamine impurity pattern. Such an impurity pattern is a result of an incomplete cleaning-up process – typical for illicit manufacturing – when producing the drug. The manufacturing process can be divided into three steps: (1) choosing a recipe for how to produce; (2) producing amphetamine oil; and finally (3) precipitating the amphetamine from the oil.

The impurity pattern of the amphetamine will depend on the recipe itself, the conditions used for the synthesis, the precipitation process and the method of cleaning-up. The impurity profile is a chromatogram of around 150 different contaminants, of these contaminants 26 have been used by several European countries in police intelligence work to link manufacturers of illicit drugs [1]. However, the linkage methods used are investigative and not evaluative.   

The issue addressed when two specific seizures are to be compared, and the results are going to be used in the court of law, is whether they originate from the same precipitation batch.  When this is true the impurity patterns of the two seizures are in general expected to be similar, at least for stable contaminants. This is a less expected result if the seizures originate from different batches.

Interpretation of observed similarities and differences between the impurity patterns of two seizures is still to a large extent based on subjective judgements where in Sweden the experiences of two forensic experts are used. In this presentation we show how the so-called multivariate kernel likelihood ratio approach [2] can be used for this interpretation. From a designed experiment comprising several recipes, the variance components for a subset or for a lower-dimensional projection of all contaminants are estimated and likelihood ratios can then be easily calculated. A cross-validatory study shows high sensitivity as well as high specificity of the likelihood ratios.

Keyword
forensic science, Bayesian inference, multivariate distribution, drugs profiling
National Category
Probability Theory and Statistics
Identifiers
urn:nbn:se:liu:diva-118545 (URN)
Conference
9th International Conference on Forensic Inference and Statistics (ICFIS2014)
Available from: 2015-06-01 Created: 2015-06-01 Last updated: 2015-06-01
Nordgaard, A. (2014). Värdering och rapportering av forensiska resultat vid SKL. In: : . Paper presented at DNA.bevis og Statistikk.
Open this publication in new window or tab >>Värdering och rapportering av forensiska resultat vid SKL
2014 (Swedish)Conference paper, Oral presentation only (Other (popular science, discussion, etc.))
National Category
Probability Theory and Statistics Law and Society
Identifiers
urn:nbn:se:liu:diva-118549 (URN)
Conference
DNA.bevis og Statistikk
Available from: 2015-06-01 Created: 2015-06-01 Last updated: 2015-06-01
Nordgaard, A. (2013). Activity level and evaluative reports on forensic science evidence. In: : . Paper presented at FORSTAT 2013. 7th workshop on forensic evidence and statistical evaluation.
Open this publication in new window or tab >>Activity level and evaluative reports on forensic science evidence
2013 (English)Conference paper, Oral presentation only (Other academic)
Keyword
forensic science, Baysian hypothesis testing
National Category
Probability Theory and Statistics Law and Society
Identifiers
urn:nbn:se:liu:diva-118551 (URN)
Conference
FORSTAT 2013. 7th workshop on forensic evidence and statistical evaluation
Available from: 2015-06-01 Created: 2015-06-01 Last updated: 2015-06-01
Nordgaard, A., Hedell, R. & Ansell, R. (2012). Assessment of forensic findings when alternative explanations have different likelihoods—“Blame-the-brother”-syndrome. Science & justice, 52(4), 226-236
Open this publication in new window or tab >>Assessment of forensic findings when alternative explanations have different likelihoods—“Blame-the-brother”-syndrome
2012 (English)In: Science & justice, ISSN 1355-0306, E-ISSN 1876-4452, Vol. 52, no 4, p. 226-236Article in journal (Refereed) Published
Abstract [en]

Assessment of forensic findings with likelihood ratios is for several cases straightforward, but there are a number of situations where contemplation of the alternative explanation to the evidence needs consideration, in particular when it comes to the reporting of the evidentiary strength. The likelihood ratio approach cannot be directly applied to cases where the proposition alternative to the forwarded one is a set of multiple propositions with different likelihoods and different prior probabilities. Here we present a general framework based on the Bayes' factor as the quantitative measure of evidentiary strength from which it can be deduced whether the direct application of a likelihood ratio is reasonable or not. The framework is applied on DNA evidence in forms of an extension to previously published work. With the help of a scale of conclusions we provide a solution to the problem of communicating to the court the evidentiary strength of a DNA match when a close relative to the suspect has a non-negligible prior probability of being the source of the DNA.

Place, publisher, year, edition, pages
Elsevier, 2012
Keyword
Evidence value, Bayes' factor, Multiple propositions, Scale of conclusions, DNA profiles, Relatives
National Category
Probability Theory and Statistics Law and Society
Identifiers
urn:nbn:se:liu:diva-79765 (URN)10.1016/j.scijus.2011.12.001 (DOI)000311920000004 ()
Available from: 2012-08-13 Created: 2012-08-13 Last updated: 2017-12-07
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