FRSC1030 Foundations in Forensic Science Chapter 2

Key Terms from chapter 2

Abductive reasoning

Gathering what is known and using this information to develop the simplest and most likely explanation. How different pieces of evidence are integrated into the most plausible theory regarding how something happened.

Admissibility

Formal acceptance of something in a legal context, commonly in relation to evidence. Used to ensure that only reliable and relevant scientific information is considered in court.

Between-sample variation

The variation between portions of samples being analyzed, or between the averages or means of different samples. 

Black box studies

A way of determining error rates, usually extensive studies in which the method used to complete a test is not critical; instead, the focus is on the result of the analysis compared to the accepted correct result. 

Circumstantial evidence

Evidence used to infer additional information.

Continuous variables

Variables without limits, such as percentages, the weight of a pill, the length of a bone. There is no set number of outcomes or categories, the result can be any number.

Daubert standard

A method used by courts to determine whether or not expert testimony should be admissible at trial. The 5 criteria are : whether the method can be or has been tested, whether the method has been subject to peer review and publication, the known or potential rate of error, the existence and maintenance of standards or controls, and the degree to which the method has been generally accepted in the scientific community.

Daubert trilogy

Three civil cases that significantly impacted how jurisdictions addressed the admissibility of evidence: GE v. Joiner, Kumho Tire v. Carmichael, and Daubert v. Merrell Dow Pharmaceuticals.

Deductive reasoning

A type of reasoning that uses core concepts and general premises to draw specific, certain conclusions using logical inference. Also called inference.

Direct evidence

Evidence or information that speaks unambiguously about a fact in question and requires no addition inference.

Discrete variables

Variables with a limited number of outcomes, such as shoe size, blood type, and fingerprint patterns. They can be labeled as numbers, but they’re categories. 

Error rate

Quantitative measurment describing how often a method produces an incorrect result. It can be a complex metric to obtain, and results are often controversial.

Exclusion / exclusive evidence

Evidence that excludes a suspect during an investigation. Also known as exculpatory evidence.

Exculpatory evidence

A category of evidence that, with its presence, excludes a person of interest as a source, and thus tends to exonerate them. Also known as exclusive evidence.

Federal Rules of Evidence

A document that governs the admission or exclusion of evidence in most proceedings in the United States courts.

Frequency database

A collection of data that organizes information based on how often specific values or events occur. DNA databases are one example, with discrete variables. Databases such as fingerprints and firearm markings are characterized mathematically.

Frye standard

A legal rule used in past courts to determine the admissibility of evidence by requiring that the scientific principles or methods used are “generally accepted” as reliable by the scientific community.

Gatekeeper

One of a judge’s roles in court, the responsibility to determine if scientific evidence is relevant or reliable.

Gaussian distribution

Also called a normal distribution, a probability distribution that appears as a bell curve when graphed, signifying that the mean and the median are in the middle of the distribution.

General acceptance

The criteria that governed the admissibility of scientific evidence in courts before the Daubert standard was created, meaning that the method or theory presented in court was supported by a significant portion of the relevant scientific community.

Histogram

A type of chart that plots the distribution of a numeric variable’s values as a series of bars that cover a range of numeric values, in which a bar’s height indicates the frequency of data points within that range.

Inclusion / inclusive evidence

Evidence that includes, or does not exclude, a person of interest in an investigation. Also known as inculpatory evidence.

Inconclusive

A result signifying that no conclusion could be reached from a comparitive analysis of evidence.

Inculpatory evidence

Also known as inclusive evidence, evidence that, with its presence, includes a person as a source and thus tends to incriminate them.

Inductive reasoning

Reasoning that uses existing data to make predictions and generalizations, and helps propose ideas or hypotheses that can be tested and checked using deductive reasoning. 

Inference

Also called deductive reasoning, a type of reasoning that uses core concepts and general premises to draw specific, certain conclusions using logical inference.

Known sample

A sample for which the analysts or investigators know the source, used to compare evidence samples from crime scenes.

Locard’s exchange principle

The concept that “every contact leaves a trace”, and explains how physical evidence can be created and how it can be used to recreate an event or sort out different versions of an event. According to the principle, contact or interaction between people or between a person and a place inevitably produces an exchange of material between them.

Normal distribution

Also called a Gaussian distribution, a probability distribution that appears as a bell curve when graphed, signifying that the mean and the median are in the middle of the distribution.

Objective

Information and data that is fact-based and often can be expressed numerically, and is easily testable.

Opinion evidence

Testimony, when a scientist will offer their opinion as part of the body of evidence considered in a case

Physical evidence

Tangible evidence, such as a bloody shirt, fibers, a blood sample, or a fingerprint

Probability

A mathematical discipline that determines how likely an event is to occur on a scale of 0-1.

Probability density function (PDF)

A function that describes the likelyhood of a continuous random variable falling within a specific range, not at a single point. 

QK comparison

A comparison between a questioned (Q) sample and a known (K) sample, that produces one of three results: exclusion, inclusion, or inconclusivity.

Questioned sample

The sample being compared to a known sample, a piece of evidence whose origin or authenticity is unknown or disputed

Relative standard deviation

A statistical measurement that expresses the standard deviation as a percentage of the mean to quantify the precision or variability of a data set.

Rules of evidence

Rules designed to ensure that only reliable and relevant scientific information is considered.

Statistics

Techniques used to study data collections, such as those found in databases

Subjective

Information that is subject to personal perceptions and outlooks and would be considered an opinion.

Successive classification

Classification that starts broad, then gets progressively more specific. Each categorization results in fewer potential substances.

Testimonial evidence

A statement made by a witness, either spoken or written, offered as proof of what they say is true. It’s considered direct evidence because it comes from a person describing what they saw, heard, or know. 

Transfer evidence

The tangible link between two people, or a person and a place, created when they come into contact with each other and an exchange of material is produced.

Weight of evidence

A scientific and legal approach to decision-making, evaluating the totality of available information from multiple sources to reach a conclusion, where the quality of each piece of evidence determines how much it contributes.

Within-sample variation

The dispersion of data points around their group’s mean, representing the natural or random differences within a single group or sample.