Chapter 16 — 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. All impression evidence rests on a single piece of physics: - A. Heat always flows from a warmer object to a cooler one - B. When a harder surface contacts a softer one with enough force, the softer one deforms to record the harder one's shape - C. Every object emits a unique electromagnetic signature - D. Pressure is inversely proportional to area

2. A footwear impression left by a dusty shoe stepping onto clean tile is best described as: - A. A three-dimensional, negative impression - B. A two-dimensional, positive (transfer) impression - C. A cast - D. A striated toolmark

3. A cast (e.g., in dental stone) of a shoe impression in soil is: - A. A negative of the soil - B. A positive replica of the underside of the shoe - C. A photograph taken under oblique light - D. A two-dimensional lift

4. The correct order for recovering a three-dimensional footwear impression is: - A. Cast first, then photograph the cast - B. Lift electrostatically, then cast - C. Photograph (with scale and oblique light) first, then cast - D. Collect the surrounding soil, then reconstruct the print in the lab

5. The tread design molded into every shoe of a given model is an example of a: - A. Acquired (individual) characteristic - B. Class characteristic - C. Subclass artifact that excludes the source - D. Striation

6. A cut, gouge, or stone lodged in one particular shoe's tread is an example of: - A. A class characteristic - B. A tread-design feature - C. An acquired (individual) characteristic - D. A noise treatment

7. A tire impression most defensibly places at a scene: - A. A specific driver - B. A vehicle (not, by itself, a driver) - C. The time the vehicle was present - D. The make of the driver's shoes

8. Striated toolmarks (as opposed to impressed marks) are produced when: - A. The tool is pressed straight into the surface - B. The tool slides along the surface and its edge cuts a series of fine parallel lines - C. The tool is heated before contact - D. The surface is harder than the tool

9. Firearms identification, relative to general toolmark identification, is best described as: - A. A completely unrelated discipline - B. A special case of toolmark identification, sharing its method and validity debate - C. More discredited than bite marks - D. The only fully validated comparison method in the book

10. The subclass-characteristic trap in toolmark comparison is the danger that: - A. The tool is too small to leave any mark - B. Marks shared by a whole production run of tools are mistaken for an individual identification - C. The examiner cannot find the tool - D. Striations fade before casting

11. On the validity spectrum, class-level toolmark testimony ("consistent with a flat pry bar ~19 mm wide") is: - A. Discredited, like bite marks - B. Well supported and survives cross-examination - C. Identical in certainty to a single-source DNA match - D. Inadmissible in every U.S. court

12. The 2016 PCAST report's verdict on firearms/toolmark individual-source identification was that: - A. Its foundational validity is fully established by black-box studies - B. Its foundational validity as a method for individual-source identification had not been established - C. It is equivalent to DNA - D. It should never be admitted for any purpose

13. Bite-mark identification rests on a stack of premises. The one that skin as a recording medium most directly defeats is: - A. That teeth are made of enamel - B. That a bitten substrate faithfully records the dentition's distinctive features - C. That dentists exist - D. That bruises are visible

14. Why is skin an especially poor substrate for recording fine dental detail? - A. It is rigid and unchanging - B. It is elastic, mobile, and curved, it stretches and rebounds, and the injury changes (swells, spreads, fades) over time - C. It cannot be photographed - D. It records detail better than dental stone

15. The claim that "the human dentition is unique" was, on the chapter's account: - A. Demonstrated by a large, well-designed validation study - B. Asserted rather than demonstrated — never grounded by measuring how often two people are indistinguishable as expressed in a bite mark on skin - C. Proven by DNA - D. Irrelevant to bite-mark testimony

16. Under the Frye standard, bite-mark testimony was helped to stay in court by: - A. A rigorous error-rate study - B. "General acceptance" — by the small community of forensic odontologists who themselves practiced it (a circular validation) - C. The PCAST report - D. A constitutional amendment

17. Two engines drove the collapse of bite-mark analysis. They were: - A. New microscopes and faster computers - B. DNA exoneration and formal scientific review (NAS 2009 / PCAST 2016) - C. Better cameras and juror education - D. The Frye standard and the ABFO

18. When examiners were finally given bite marks of known origin in proficiency-style tests, they: - A. Agreed perfectly with one another and the ground truth - B. Disagreed with one another and with the ground truth at rates incompatible with their courtroom certainty — sometimes even on whether a mark was a human bite - C. Refused to participate - D. Outperformed DNA analysts

Short answer

19. State the four-rung hierarchy of conclusions an honest impression examiner works within (§16.1), in order, and give a one-line gloss of the two end rungs (exclusion and individual identification).

20. Explain why a single unexplained difference between a questioned and a known impression can be more powerful than a dozen points of agreement.

21. Distinguish footwear class evidence from footwear identification in terms of validity: which is closer to "manufacturing information" and well supported, and which is a "judgment about specificity" with far less error-rate research behind it?

22. In the Ray Krone case, two comparison methods reached opposite answers. Name the two methods, say which pointed at the wrong person and which corrected it, and state the one-line lesson the chapter draws ("confidence is not ____").

23. The Roy Brown case is called "the courtroom embodiment of §16.1's hierarchy of conclusions." Explain why — what did the bite-mark evidence apparently contain that, read honestly, should have driven toward exclusion?

24. In the cold case, the cabin door's pry marks support forced entry at the class level. Write one sentence an honest examiner could say on the stand about those marks, and one sentence that would overstate them.

Answer key (click to expand) **Multiple choice:** 1-B · 2-B · 3-B · 4-C · 5-B · 6-C · 7-B · 8-B · 9-B · 10-B · 11-B · 12-B · 13-B · 14-B · 15-B · 16-B · 17-B · 18-B **Short answer (model points):** **19.** In order: (1) **Exclusion** — the known source could not have made the questioned impression (wrong size/design, an unexplained difference); the cleanest, most defensible call. (2) **Class association** ("could have made / is consistent with") — questioned and known share class characteristics; the source *and every other object of its class* cannot be excluded. (3) **Association with individual characteristics** ("identification" in some labs) — enough corresponding acquired damage that the examiner concludes this source made it; the contested top rung. (4) **Inconclusive / unsuitable** — too faint, partial, or smeared to support any of the above. **20.** Agreement only *associates*, and how strongly depends on whether the agreeing features are class or individual — many objects can share class features. But a genuine, *unexplained* difference can *exclude*: if the questioned impression has a feature the known source could not have produced, the source did not make it, full stop. One clean difference can therefore settle the question that any amount of agreement only narrows. (This mirrors the exclude-vs-associate asymmetry of DNA, Chapter 7.) **21.** **Class** evidence (tread design, size) is, at bottom, *manufacturing information*: a given outsole pattern is made by one manufacturer in a finite run of sizes, so "consistent with this model and size" is well supported. **Identification** from acquired characteristics depends on the examiner's *judgment* that the corresponding random marks are numerous and specific enough to exclude every other shoe — a judgment, not a calculation, and far less studied for error rate than DNA. Class is closer to manufacturing fact; identification is a specificity judgment. **22.** The two methods were **bite-mark comparison** (at trial) and **nuclear DNA typing** (years later). The bite-mark "match" pointed at the wrong person (Krone); the DNA excluded Krone and matched another, identified man, correcting it. The lesson: **confidence is not validity** — the most persuasive courtroom exhibit can be the most wrong. **23.** By one account the bite marks displayed features inconsistent with Brown's dentition — reportedly *more upper teeth than Brown possessed*. A genuine, unexplained **difference** like that is, in any disciplined comparison, grounds for **exclusion** (the most defensible thing impression comparison does). Instead the trial testimony minimized the discrepancy to preserve a match — inverting the discipline's own logic, in which the first question is "what *differs*, and why isn't that an exclusion?" **24.** **Honest:** "The gouges and compressed profile in the doorframe are consistent with a flat pry bar of a certain width and shape; such a tool could have made them, which supports forced entry." **Overstated:** "These marks were made by the suspect's specific crowbar, to the exclusion of all other tools, proving he forced the door." (The first dates and characterizes the *act*; the second falsely names the *actor* and claims an unvalidated individual-source identification.)