Marjan Sjerps

Marjan Sjerps
University of Amsterdam | UVA · Institute of Mathematics Korteweg-De Vries

PhD

About

78
Publications
15,075
Reads
How we measure 'reads'
A 'read' is counted each time someone views a publication summary (such as the title, abstract, and list of authors), clicks on a figure, or views or downloads the full-text. Learn more
872
Citations
Additional affiliations
May 1994 - present
Netherlands Forensic Institute
Position
  • principal scientists

Publications

Publications (78)
Article
This study presents a method to derive numerical LRs for distance data from the iPhone Health app. The LR method provides a probability model for hypotheses that specify a walking distance in meters. The method is demonstrated using a hypothetical case example in which a suspected arsonist's walking route is disputed. The performance of the LR meth...
Preprint
Full-text available
Messenger RNA (mRNA) profiling can identify body fluids present in a stain, yielding information on what activities could have taken place at a crime scene. To account for uncertainty in such identifications, recent work has focused on devising statistical models to allow for probabilistic statements on the presence of body fluids. A major hurdle f...
Article
Tire marks are an important type of forensic evidence as they are frequently encountered at crime scenes. When the tires of a suspect’s car are compared, the evidence can be very strong if so-called ‘acquired features’ are observed to correspond. When only ‘class characteristics’ such as parts of the tire pattern are observed to correspond, it is o...
Article
Forensic soil comparisons can be of high evidential value in a forensic case, but become complex when multiple methods and factors are considered. Bayesian networks are well suited to support forensic practitioners in complex casework. This study discusses the structure of a Bayesian network, elaborates on the in- and output data and evaluates two...
Article
A new method for the evaluation of duct tape ends is proposed. This method is based on the breaks of the loops in the warp yarns, when duct tape with a scrim of chain-stitched warp yarns and weft-insertion is torn. After tearing, the loop at the end of each warp yarn can be in one of four states: open, closed, complex or missing. Additionally, the...
Article
Full-text available
Evaluating evidence and providing opinions are at the heart of forensic science, and forensic experts are expected to provide opinions that are based on logically sound and transparent scientific reasoning, and that honour the boundaries of their area of expertise. In order to meet these objectives, many fields of science explicitly apply Bayes' th...
Article
Messenger RNA (mRNA) profiling can identify body fluids present in a stain, yielding information on what activities could have taken place at a crime scene. To account for uncertainty in such identifications, recent work has focused on devising statistical models to allow for probabilistic statements on the presence of body fluids. A major hurdle f...
Article
Numerical likelihood-ratio (LR) systems aim to calculate evidential strength for forensic evidence evaluation. Calibration of such LR-systems is essential: one does not want to over- or understate the strength of the evidence. Metrics that measure calibration differ in sensitivity to errors in calibration of such systems. In this paper we compare f...
Article
In their paper “The evaluation of evidence for microspectrophotometry data using functional data analysis”, in FSI 305, Aitken et al. present a likelihood-ratio (LR) system for their data. We show the values generated by this system cannot be interpreted as LRs: they are ill-calibrated and should be interpreted as discriminating scores. We demonstr...
Article
Activity level evaluations, although still a major challenge for many disciplines, bring a wealth of possibilities for a more formal approach to the evaluation of interdisciplinary forensic evidence. This paper proposes a practical methodology for combining evidence from different disciplines within the likelihood ratio framework. Evidence schemes...
Article
Sampling strategy is one of the deciding factors in DNA typing success rates. Small amounts of bodily fluid traces and (skin) contact traces are currently not visualized in standard forensic practice. Trace recovery is usually based on the information available in a particular case and on the experience and ‘forensic common sense’ applied by the tr...
Article
Full-text available
This study covers an extensive experimental design that was developed for creating simulated fire debris samples under controlled conditions for the detection and identification of ignitable liquids (IL) residues. This design included 19 different substrates, 45 substrate combinations with and without ignitable liquids, and 45 different ILs from th...
Article
In forensic casework it is common that multiple pieces of evidence are obtained in a single case. For the evaluation of such evidence, one cannot simply assume that they originated from the same source. If this can be disputed, one could decide to report the evidential value of the separate pieces by computing likelihood ratios (LRs) for them separ...
Article
Full-text available
Recent leverde rechtspsycholoog prof. Peter van Koppen in een artikel 2 in dit blad stevige kritiek op rapportages van het Nederlands Forensisch Instituut (NFI). Hierbij werd één specifiek NFI-rapport over een speciaal type hamer, een tengelhamer, als voorbeeld gebruikt. In dit artikel bespreken wij deze kritiek. Kortgezegd: wij zien in het artikel...
Poster
Full-text available
In forensic casework, it is common that multiple partial DNA profiles are obtained in a single case. For the evaluation of such evidence, it is necessary to consider the possibility that they originated from different sources. One could report the evidential value of the separate profiles by computing likelihood ratios for them separately. However,...
Article
In this article, the performance of a score-based likelihood ratio (LR) system for comparisons of fingerprints with fingermarks is studied. The system is based on an automated fingerprint identification system (AFIS) comparison algorithm and focuses on fingerprint comparisons where the fingermarks contain 6–11 minutiae. The hypotheses under conside...
Article
Full-text available
In de Zoete et al. (2015) a framework for the evaluation of evidence when an individual is a suspect of two separate offenses (based on Evett et al., 2006) is implemented using a Bayesian network. Here, we extend this to situations with multiple offenders. When we have multiple offenders, new questions arise: (1) Can we distinguish between the offe...
Article
Forensic examination of fire debris evidence is a notoriously difficult analytical task due to the complexity and variability of sample composition. The use of comprehensive two-dimensional gas chromatography with mass spectrometry detection (GC × GC–MS) allows the coupling of orthogonal retention mechanisms and therefore a high peak capacity. We d...
Article
Full-text available
In forensic casework, evidence regarding the type of cell material contained in a stain can be crucial in determining what happened. For example, a DNA match in a sexual offense can become substantially more incriminating when there is evidence supporting that semen cells are present. Besides the question which cell types are present in a sample, a...
Article
Two approaches were investigated to discriminate between bell peppers of different geographic origins. Firstly, δ18O fruit water and corresponding source water were analyzed and correlated to the regional GNIP (Global Network of Isotopes in Precipitation) values. The water and GNIP data showed good correlation with the pepper data, with constant is...
Article
DNA profiles can be used as evidence to distinguish between possible donors of a crime stain. In some cases, both the prosecution and the defence claim that the cell material was left by the suspect but they dispute which cell type was left behind. For example, in sexual offense cases the prosecution could claim that the sample contains semen cells...
Article
In this study, the application of comprehensive two-dimensional (2D) gas chromatography (GC × GC) in forensic science is reviewed. The peer-reviewed publications on the forensic use of GC × GC and 2D gas chromatography with mass spectrometric detection (GC × GC-MS) have been studied in detail, not only to provide an overview, but also to analyze an...
Article
Accurate analysis of chromatographic data often requires the removal of baseline drift. A frequently employed strategy strives to determine asymmetric weights in order to fit a baseline model by regression. Unfortunately, chromatograms characterized by a very high peak saturation pose a significant challenge to such algorithms. In addition, a low s...
Article
Taroni et al. (in press) discuss the controversial issue of parameter uncertainty in the context of forensic evidence evaluation. Although we share with the authors the main idea that the likelihood ratio (LR) framework is the best method for evaluating forensic evidence, we have a different view on this issue. The core question is: does it make se...
Poster
Full-text available
DNA profiles can be used as evidence to distinguish between possible donors of a crime stain. In some cases, both the prosecution and the defence claim that the cell material was left by the suspect but they dispute which cell type was left behind. For example, in sexual offense cases the prosecution could claim that the sample contains semen cells...
Article
Forensic chemical analysis of fire debris addresses the question of whether ignitable liquid residue is present in a sample and, if so, what type. Evidence evaluation regarding this question is complicated by interference from pyrolysis products of the substrate materials present in a fire. A method is developed to derive a set of class-conditional...
Article
Full-text available
When two or more crimes show specific similarities, such as a very distinct modus operandi, the probability that they were committed by the same offender becomes of interest. This probability depends on the degree of similarity and distinctiveness. We show how Bayesian networks can be used to model different evidential structures that can occur whe...
Article
Full-text available
In deze bijdrage wordt het gebruik van schakelbewijs in strafzaken vanuit twee verschillende en elkaar soms tegensprekende gezichtspunten beschreven. Naast een juridische beschouwing zal bezien worden hoe schakelbewijs vanuit een kanstheoretische invalshoek benaderd en geduid kan worden. Met deze bijdrage hopen wij inzichtelijk te maken dat verschi...
Article
Forensic DNA casework is currently regarded as one of the most important types of forensic evidence, and important decisions in intelligence and justice are based on it. However, errors occasionally occur and may have very serious consequences. In other domains, error rates have been defined and published. The forensic domain is lagging behind conc...
Article
We present a novel algorithm for probabilistic peak detection in first-order chromatographic data. Unlike conventional methods that deliver a binary answer pertaining to the expected presence or absence of a chromatographic peak, our method calculates the probability of a point being affected by such a peak. The algorithm makes use of chromatograph...
Article
Full-text available
When a Y-chromosomal and a (partial) autosomal DNA profile are obtained from one crime sample, and both profiles match the suspect's profiles, we would like to know the combined evidential value. To calculate the likelihood ratio of observing the autosomal and Y-chromosomal DNA profiles combined, we need to know the conditional random match probabi...
Conference Paper
Full-text available
When visible on a fingermark, the general pattern maintains its importance in the fingerprint examination procedure, since the difference between the general pattern of a fingermark and a fingerprint is sufficient for exclusion. In the current work, the importance of the general pattern is extended by evaluating the strength of evidence of a match...
Article
Full-text available
Experts providing evidence in legal cases are universally recommended to be transparent, particularly in their reasoning, so that legal practitioners can critically check whether the conclusions are adequately supported by the results. However, when exploring the practical meaning of this recommendation it becomes clear that people have different t...
Article
Full-text available
The Hamer contribution reveals a lot of the common misperceptions surrounding the issues in R v. T. While the paper risks adding to the confusion of the uninformed reader, we will use it to list and address such misperceptions in this reaction. We acknowledge that the author will in some cases have described misconceptions held by others rather tha...
Chapter
One of the central questions in a legal trial is whether the suspect did or did not commit the crime. It will be apparent that absolute certainty cannot be attained. Because there is always a certain degree of uncertainty when interpreting the evidence, none of the evidence rules out all hypotheses except one. The central question should therefore...
Article
In dit artikel beschouwen we verschillende soorten databankmatches tussen het DNA-profiel van een spoor en dat van een persoon. Ter verduidelijking geven wij hieronder alvast de definities van de gehanteerde termen: echte match: de persoon is de donor van het spoor; toevallige match (vals positieve match): de persoon is niet de donor van het spoor;...
Article
Full-text available
The judgment of the Court of Appeal in R v T [1] raises several issues relating to the evaluation of scientific evidence that, we believe, require a response. We, the undersigned, oppose any response to the judgment that would result in a movement away from the use of logical methods for evidence evaluation. A paper in this issue of the Journal [2]...
Article
Als bij het onderzoek in een strafzaak de DNA-profielen van een spoor en een verdachte matchen wordt dit algemeen beschouwd als zeer sterk bewijsmateriaal dat het spoor afkomstig is van de verdachte. Maar geldt dit ook als deze persoon op een speciale manier als verdachte in beeld is gekomen, namelijk doordat met deze persoon een match in de DNA-da...
Article
We argue that it is, in principle, not difficult to deal with selection effects in forensic science. If a suspect is selected through a process that is related to the forensic evidence, then the strength of the evidence will be compensated by very small prior odds. No further correction is necessary. The same is true for so-called data-dependent hy...
Article
Anti-doping is currently viewed as a forensic science. However, close examination shows that the statistical treatment of evidence is inconsistent with that view. Here it is insisted that anti-doping researchers should conform to certain statistical standards from forensic science.
Article
Full-text available
The introduction of DNA evidence has transformed human individualization in criminal litigation, but it also introduced daunting statistical, philosophical and practical problems into the process. The current practice in many legal cases is that a forensic expert reports a match probability or a likelihood ratio. However, the value of the likelihoo...
Article
Even though trace evidence is becoming more and more important in legal cases, only little is known about the influence of task and context factors on comparative judgments. In the present study we investigated how expectations and complexity affect shoe print examinations and to what extent differences exist between beginners and experienced exami...
Article
Als gevolg van de toepassing van steeds verfijnder technieken zijn de mogelijkheden om met het oog niet of nauwelijks waarneembare sporen te analyseren de laatste jaren weliswaar aanzienlijk toegenomen maar daar staat tegenover dat de bewijswaarde van het gevonden DNA-materiaal eerder een ontwikkeling in omgekeerde richting laat zien. Gevoeliger an...
Article
Statistics plays a crucial role in obtaining, interpreting and reporting results. Sampling, statistical quality control, chemometrics, biometrics, design of experiments, and the Bayesian framework for interpreting evidence are areas of statistics that are of key importance to many forensic scientists. However, most forensic scientists need addition...
Article
In legal environmental control, solid wastes are sampled to determine whether the mean concentrations of contaminants meet the regulatory standard. Current sampling and statistical testing procedures for solid wastes often rely on assumptions about the heterogeneity of the contaminants and on the assumption that the frequency distribution of the da...
Article
Full-text available
In this article we respond to Dawid, Balding, Triggs and Buckleton.
Article
Does the evidential strength of a DNA match depend on whether the suspect was identified through database search or through other evidence ("probable cause")? In Balding and Donnelly (1995, Journal of the Royal Statistical Society, Series A 158, 21-53) and elsewhere, it has been argued that the evidential strength is slightly larger in a database s...
Article
DNA profiling has become one of the most powerful forensic techniques that is used in criminal investigations to identify suspects. Moreover, scientific DNA evidence has become an important component in criminal trials. The interpretation of DNA evidence involves many statistical and probabilistic aspects, which have been the subject of fierce deba...
Article
The Bayesian framework is a useful logical concept which potentially applies to a large number of areas in forensic science, including speaker identification. According to this line of reasoning, the forensic expert is not in a position to draw conclusions about the probability of a hypothesis, e.g. the probability that the unknown speaker on a tap...
Article
In legal control, solid wastes are sampled to determine if particular concentrations of contaminants are below threshold levels. If the threshold is exceeded, the material is considered hazardous and constraints are placed on its handling and disposal. This procedure requires a uniform sampling and hypothesis testing protocol that gives reliable re...
Article
This paper addresses the question of the number of recovered microtraces (hairs, fibres, glass, paint, etc.) to be measured in forensic casework. If the measurement method allows for identification with absolute certainty, the appropriate probability model is identified as sampling without replacement from an urn containing balls of two colours, as...
Article
If the DNA profiles of a crime stain and the reference sample from the suspect do not match, the suspect is excluded as the donor of the crime stain. However, in some situations the DNA evidence can suggest that a close relative of the suspect might match the stain, in particular when the reference sample from the suspect and the crime stain share...
Article
To introduce a duplex PCR system consisting of the STR loci D21S11 and HUMFIBRA in forensic identity testing we analysed a Dutch Caucasian database of 205 individuals. The combined power of discrimination of the two loci is 0.9978 and there was no evidence for linkage equilibrium between the two loci (p=0.91). However, we noticed departure from Har...
Article
To introduce a duplex PCR system consisting of the STR loci D21S11 and HUMFIBRA in forensic identity testing we analysed a Dutch Caucasian database of 205 individuals. The combined power of discrimination of the two loci is 0.9978 and there was no evidence for linkage equilibrium between the two loci (p = 0.91). However, we noticed departure from H...
Chapter
Population genetic studies show differences within and between racial groups for the HLADQA1 locus1 2. The chi-square test is a relatively simple test which is often used when comparing population samples. However, when a large number of samples are compared, it is difficult to get a clearly structured overall picture. A quick overview of the dista...
Article
We report on a Dutch population study of the STR loci HUMTHO1, HUMFES/FPS, HUMVWA31/1, and HUMF13A1, in which we used multiplex amplification and automated fragment detection. Genotype and allele frequencies showed no deviation from Hardy-Weinberg and linkage equilibrium. The improved Bonferroni procedure was used to combine the results of several...
Article
To introduce the loci LDLR, GYPA, HBGG, D7S8, and GC (PM loci) in Dutch forensic identity testing, allele and genotype frequencies were determined in a Dutch Caucasian population sample, which had previously been typed for the HLADQA1 locus [12]. All 6 loci met Hardy-Weinberg equilibrium expectations, and there is little evidence for association be...
Article
When resources are patchily distributed, animals have to decide when to leave a patch to find a new one. We model this leaving decision for any number n≥2 of animals per patch as a new version of the war of attrition. First, we consider a particular patch and assume that the animals get a fixed gain rate after leaving this patch. In this case, the...
Article
Many insect species lay their eggs according to a clumped distribution, which causes food shortage among the larvae. To avoid starvation, at least some larvae have to migrate to another plant at some stage. Even though this migration involves a high mortality risk, larvae (of, for example, the cinnabar moth) often leave before their host plant is d...
Article
When two insects oviposit on the same host, their abilities to detect the other female's clutch and assess its size crucially determine their optimal clutch sizes. If detection is impossible, the optimal clutch sizes are simply found by pure maximization, and if only size assessment is impossible, they are a Nash equilibrium pair. This paper compar...
Article
A puzzling phenomenon in insect oviposition is the variety of egg distributions over plants. A clumped distribution can cause food competition among the offspring, and consequently risky migration to other plants. On the other hand, egg clumping can initially be advantageous. To examine under which conditions egg clumping is optimal, we studied the...

Network

Cited By