Chapter 19 — Self-Check Quiz

24 questions: multiple choice and short answer. Try them closed-book. The answer key is in the collapsed block at the bottom.

Multiple choice

1. Trace evidence is best defined as physical evidence that is: - A. Always biological in origin - B. Found in small or microscopic quantities and transferred between people, objects, and environments by contact - C. Only ever class evidence with no investigative value - D. Visible to the naked eye at every scene

2. Trace evidence is the most direct courtroom application of: - A. The random match probability - B. The Daubert standard - C. Locard's exchange principle - D. The prosecutor's fallacy

3. Transfer and persistence refer, respectively, to: - A. How material moves between surfaces on contact, and how long it remains afterward - B. How long material remains, and how it is packaged - C. The color of a fiber, and its polymer type - D. The age of a hair, and its body region

4. Secondary transfer matters because it means a trace found on a suspect: - A. Must have come directly from the victim - B. Need not have come from the victim directly — it could have moved through an intermediate surface or person - C. Is always contamination introduced by the lab - D. Cannot be recovered by taping

5. The single most reliable thing a microscopic hair examination can establish is: - A. The exact identity of the person who shed it - B. Whether the hair is human or animal - C. The time the hair was shed - D. The suspect's ancestry to a certainty

6. The features an examiner reads from a hair (color, diameter, medulla type, body region) are: - A. Individual characteristics that point to one person - B. Class characteristics shared by a large number of people - C. A validated statistical profile with a known frequency - D. Sufficient, on their own, for a courtroom "match"

7. Why can a visual hair "consistency" not be expressed as a likelihood ratio? - A. Likelihood ratios are illegal in court - B. There is no validated frequency for how rare any combination of hair features is in the population — no denominator exists - C. Hairs are too small to measure - D. The comparison microscope cannot magnify enough

8. In April 2015, the FBI publicly admitted that, in the large majority of reviewed cases, its examiners' microscopic-hair testimony had: - A. Been understated to protect defendants - B. Exceeded the limits of the science by overstating the strength of an association - C. Been fabricated entirely with no examination performed - D. Correctly identified every defendant

9. What finally forced the reckoning over microscopic hair comparison was: - A. A new federal statute - B. Post-conviction DNA testing that excluded people whose convictions had rested partly on hair "matches" - C. The invention of the comparison microscope - D. A change in the rules of grammar

10. Santae Tribble and Kirk Odom are cited in the chapter as examples of: - A. Fiber-evidence successes - B. People exonerated after convictions that rested partly on hair testimony DNA later overturned - C. Forensic examiners who testified at the FBI - D. Fictional persons of interest in the cold case

11. On the validity spectrum, microscopic hair comparison for associating a hair with a specific person sits: - A. Above single-source DNA - B. Near the bottom — below contested toolmarks, above only fully discredited methods like bite-mark matching - C. At the exact center, equal to fingerprints - D. Off the spectrum entirely because it is perfectly reliable

12. A fiber is: - A. A single human hair - B. The smallest unit of a textile, natural or manufactured - C. A type of gunshot residue - D. A pollen grain

13. Compared with hair comparison, the fiber examiner's toolkit is described as "genuinely scientific where hair's was not" mainly because it rests on: - A. The examiner's years of experience alone - B. Objective, reproducible measurements — polymer type, cross-section, diameter, and dye chemistry/color spectrum - C. A larger comparison microscope - D. The examiner knowing which fiber is the suspect's

14. Microspectrophotometry strengthens fiber analysis by: - A. Replacing the microscope entirely - B. Recording a fiber's color as a full absorption spectrum rather than a subjective adjective, so two fibers can be cleanly excluded if their spectra differ - C. Proving a fiber came from one unique garment - D. Measuring the suspect's DNA

15. The strength of a fiber association scales above all with: - A. The examiner's confidence - B. The rarity of the fiber and the number of independent (ideally two-way) transfers - C. How blue the fiber is - D. The length of the trial

16. A single cotton fiber linking a suspect to a scene is weak evidence because: - A. Cotton cannot be analyzed - B. Cotton is extremely common, so an enormous number of sources could account for it - C. Cotton dissolves under a microscope - D. Cotton is always contamination

17. The comparison microscope is two microscopes joined by an optical bridge so that one eyepiece presents: - A. A single specimen at very high magnification - B. Two specimens side by side in one split field of view, at matched magnification and lighting - C. A digital photograph of a database hit - D. A DNA electropherogram

18. The chapter's chief warning about the comparison microscope is that it is: - A. Useless for fibers - B. Built to find agreement, so a motivated observer who knows which specimen is the suspect's will tend to see the similarities they expect — powerful for excluding, dangerous for confirming - C. Too expensive for most labs - D. Incapable of comparing striations

19. Almost all trace evidence (fibers, paint, glass, soil) is: - A. Individual evidence that points to one source - B. Class evidence that narrows the field but rarely points to one source - C. Worthless in court - D. As strong as a single-source DNA match

20. A torn-edge physical (jigsaw) match, or a glass fragment that fits back into a broken pane, can be near-individualizing because it: - A. Has a known population frequency - B. Reconstructs a unique break or fit - C. Was measured by microspectrophotometry - D. Came from a rare dye lot

21. In the cold case, the synthetic fibers on the victim's shirt most defensibly establish that: - A. Roy Keller's jacket was definitely the source, to the exclusion of all others - B. A common-type fiber consistent with Keller's jacket — and a large number of other dark polyester garments — was present; the jacket cannot be excluded as a source - C. Keller was present at the time of death - D. The hair and the fiber came from the same person

22. In the cold case, the hair recovered from the victim's collar is: - A. Matched to Keller by microscopic comparison - B. Rootless, carries no statistical weight from its class characteristics, and is routed to mitochondrial DNA, which can exclude but not individualize - C. Used to prove the time of death - D. Discarded as worthless

23. A precise output such as "there is a 1-in-1,000 chance this hair came from someone else" is: - A. The gold-standard form of a hair result - B. A fabrication — no validated frequency for hair features exists, so the number has no study behind it - C. Required by the FBI - D. More reliable than a DNA match

24. The chapter's two honest cautions about the hair scandal are that the review faulted: - A. The verdicts in every case, proving universal innocence - B. The testimony (overstatement), not necessarily every verdict — and that modern hair work done within its limits and paired with DNA is not the discredited practice - C. Only the comparison microscope's manufacturer - D. Fiber evidence as much as hair evidence

Short answer

25. In two sentences, explain why the defensible ceiling of a visual hair examination is exclusion and non-exclusion, not a "match."

26. Name three sources by which trace evidence can be manufactured (contaminated into existence) in a lab, and state the practice that guards against each.

27. Why can a fiber association sometimes carry real probabilistic weight while a hair "consistency" carries almost none on its own? Give the two reasons the chapter stresses.

28. Explain, in one or two sentences, why the same comparison microscope is a strength for fibers and a trap for hair when the examiner knows which specimen is the suspect's.

29. In the cold case, write one sentence an honest examiner could say on the stand about the fibers on the victim's shirt, and one sentence that would overstate them.

30. State the single transferable lesson the chapter draws from the hair scandal — the sentence about "a method with no measured error rate" — and name the later chapter where it becomes the thesis.

Answer key (click to expand) **Multiple choice:** 1-B · 2-C · 3-A · 4-B · 5-B · 6-B · 7-B · 8-B · 9-B · 10-B · 11-B · 12-B · 13-B · 14-B · 15-B · 16-B · 17-B · 18-B · 19-B · 20-B · 21-B · 22-B · 23-B · 24-B **Short answer (model points):** **25.** Visual examination reads only *class* characteristics (human/animal, body region, color, diameter, medulla type) shared by an enormous number of people, and there is no validated frequency for any combination of them, so the comparison has no denominator and cannot be turned into a number. The honest endpoints are therefore "excluded" (a real difference rules the person out) or "cannot be excluded, along with many others" — never "match," "identical," or any near-statistical claim. **26.** Any three, e.g.: (a) **a hair shed by the examiner** onto the item → take known elimination samples from everyone who handled the scene and examine in clean spaces; (b) **a fiber carried between items on shared forceps/tools** → use clean or dedicated tools and handle one item at a time; (c) **cross-contamination between suspect and victim items** that passed through the same room or gloved hands → collect, package, and examine victim, suspect, and scene items *separately*, ideally by different people in different spaces. The unifying rule: keep sources physically and procedurally apart, because a lab-manufactured "match" looks exactly like a real one. **27.** (1) **Objective measurement / a denominator.** A fiber's identity rests on reproducible physical properties (polymer, cross-section, diameter, dye spectrum) that can *exclude* cleanly and characterize precisely, and the *rarity* of an unusual fiber can be assessed; hair has no validated population frequency, so "consistent" has no number behind it. (2) **Rarity and number of transfers.** A fiber association's weight scales with how rare the fiber is and how many independent (ideally two-way) transfers there are; a single common hair "consistency" has neither rarity nor a quantifiable basis. **28.** Side-by-side viewing under matched conditions is built to reveal agreement, which is exactly what fiber analysis wants (it makes *exclusion* of differing fibers decisive and the comparison rests on measured properties); but for hair, where there is no measurement and no frequency, the same vivid impression of "these go together" lets a motivated observer see expected similarities and discount differences — turning the instrument into a bias amplifier rather than a measuring tool. **29.** **Honest:** "The questioned and known fibers are indistinguishable in polymer type, cross-section, diameter, and color; this is a *common* fiber type, it is class evidence, and I cannot exclude the jacket as a source — along with a large number of other dark polyester garments." **Overstated:** "These fibers prove the defendant's jacket was pressed against the victim." **30.** **Lesson:** *A method with no measured error rate, operated inside a system that knows the answer it wants, will drift toward that answer and call the drift science.* The chapter notes this "is the thesis of **Chapter 31**" (cognitive bias in forensic analysis).