Chapter 30 — Self-Check Quiz

26 questions: multiple choice and short answer. Try them closed-book. The answer key is in the collapsed block at the bottom. Several short-answer items ask you to write the sentence an honest expert would say — that is the chapter's core skill, and it rewards saying it out loud.

Multiple choice

1. The defining difference between an expert witness and an ordinary ("lay") witness is that the expert: - A. Is always paid more - B. May offer opinions and conclusions, not merely firsthand observations - C. Cannot be cross-examined - D. Decides the verdict

2. Voir dire of a proposed expert is: - A. The closing argument - B. The preliminary examination to decide whether the witness may testify as an expert at all - C. The questioning by the side that called the witness, on the merits - D. The jury's deliberation

3. Under Kumho Tire, a court deciding whether to qualify an expert must ask about: - A. The general impressiveness of the witness's résumé - B. The specific opinion offered, in the specific field, not just the witness's overall stature - C. Only the number of years of experience - D. Whether the opposing side objects

4. A witness can be readily "qualified as an expert in forensic odontology" and still give testimony the discipline cannot support. This shows that qualification is a statement about: - A. The validity of the method - B. Whether the opinion is correct - C. The witness's standing, which says almost nothing about whether the method is valid - D. The error rate of the technique

5. On direct examination of an expert, the chief danger to honesty is: - A. The hostile opposing attorney - B. The judge's questions - C. The friendly attorney inviting an overstatement through the phrasing of the question - D. The court reporter

6. "The likelihood ratio is a million, which basically means there's a million-to-one chance it's him" is an example of: - A. An honest, complete statement of the result - B. The prosecutor's fallacy in plain English — a transposed conditional - C. The defense fallacy - D. A permissible courtroom shortcut

7. A competent cross-examiner of a DNA analyst usually does not: - A. Attack the validity of the underlying chemistry head-on - B. Probe the assumptions and inputs of the calculation - C. Ask whether the sample was degraded, low-template, or a mixture - D. Ask what the analyst was told before the analysis

8. The single most productive line of forensic cross-examination targets the witness's: - A. Educational background - B. Certainty - C. Salary - D. Courtroom demeanor

9. The ultimate-issue rule, in its modern American form, means an expert: - A. May never say anything that bears on guilt - B. May testify directly that the defendant is guilty - C. May state an opinion that embraces an ultimate issue but may not usurp the jury by testifying to guilt - D. May not testify at all on contested matters

10. "To a reasonable degree of scientific certainty" is singled out in §30.4 as dangerous because it is: - A. A precise statistical measure - B. A legal formula with no defined numerical meaning, which can launder the absence of validation into the appearance of certainty - C. Required by the Federal Rules of Evidence - D. A phrase only used by defense experts

11. Overstatement is described as more insidious than a blatant "he's guilty" because it: - A. Is always intentional - B. Produces the effect of an ultimate-issue opinion without ever saying the forbidden words - C. Is permitted by Daubert - D. Only occurs in DNA cases

12. The FBI's review of microscopic hair comparison (Chapter 19) found that examiners had overstated the evidence "not by lying about what they saw," but by: - A. Fabricating samples - B. Letting the jury hear "consistent with" as "identical to" - C. Refusing to testify - D. Using the wrong microscope

13. Communicating uncertainty is threaded between two opposite failure modes: - A. Speaking too fast and too slow - B. Overstatement (rounding up into certainty) and uselessly vague hedging (offering nothing to weigh) - C. Honesty and dishonesty - D. Direct and cross-examination

14. A verbal scale that converts a large likelihood ratio into "very strong support" stays honest only if the witness: - A. Drops the number entirely - B. Always completes it with "...for this proposition over that one" - C. Rounds it up to "proof" - D. Lets the jury decide what "very strong" means

15. The hired-gun problem is best described as: - A. A problem caused entirely by a few corrupt experts - B. The structural pressure — built into adversarial, party-paid testimony — that pulls even honest experts toward the retaining side's conclusion - C. A rule of evidence - D. A type of cross-examination

16. Adversarial allegiance refers to: - A. The lawyer's duty to argue for the client - B. The documented tendency for experts to reach conclusions favoring whichever side engaged them, even when they believe themselves objective - C. A formal oath experts take - D. The jury's loyalty to the prosecution

17. "I am an objective scientist" is described in §30.6 as: - A. A complete defense against bias - B. A symptom, not a defense — because the bias is unconscious, and confidence in immunity is itself a warning sign - C. Irrelevant to forensic testimony - D. The correct thing to say on cross

18. The expert's overriding duty is to: - A. The party who retains and pays them - B. Their own laboratory - C. The court (and the truth), which outranks any loyalty to a side - D. The jury foreperson

19. In the book's statistical language, the expert owns the __ and must never claim the ____: - A. prior; likelihood ratio - B. likelihood ratio; posterior (probability of guilt) - C. verdict; evidence - D. error rate; sample

20. In Figure 30.1, the only thing that differs between Witness A and Witness B is: - A. The laboratory result - B. The likelihood ratio - C. The words each chose on direct (certainty vs. strength of support) - D. The judge

Short answer

21. In one sentence each, distinguish direct examination from cross-examination by (a) who conducts each and (b) the characteristic kind of question (open-ended vs. leading).

22. Explain why "the best defense against a withering cross-examination is a candid direct," using Figure 30.1's two witnesses to make it concrete.

23. Name three of the six cross-examination "seams" from §30.3 that target something other than the underlying science, and for each, name the upstream chapter where that vulnerability is actually created.

24. State the one rule about a verb that simultaneously defeats overstatement, survives cross-examination, and avoids the ultimate-issue error.

25. Write one sentence a DNA analyst may say about a mixture result, and one sentence the analyst may not say — and name which line the forbidden sentence crosses.

26. In the cold case, why does no witness testify that Roy Keller is guilty? Name whose job that final step is, and what they must weigh to take it.

Answer key (click to expand) **Multiple choice:** 1-B · 2-B · 3-B · 4-C · 5-C · 6-B · 7-A · 8-B · 9-C · 10-B · 11-B · 12-B · 13-B · 14-B · 15-B · 16-B · 17-B · 18-C · 19-B · 20-C **Short answer (model points):** **21.** **(a)** *Direct* is conducted by the attorney who *called* the witness; *cross* is conducted by the *opposing* attorney (the side that did not call them). **(b)** Direct uses largely *open-ended* questions ("What did you do? What does that mean?") that let the witness explain; cross uses largely *leading* questions that suggest their own answer and confine the witness toward "yes"/"no," letting the examiner control the witness. **22.** The two witnesses in Figure 30.1 hold the *identical* likelihood ratio; nothing about the science differs. Witness A claimed *certainty* on direct, so the cross-examiner converts every honest limitation of the method (you can't exclude everyone on Earth; the error rate is non-zero) into a visible *retreat* — each forced "no" looks like a discovered weakness. Witness B stated those *same* limitations *first*, as features of honest science, so the cross-examiner's questions strike conclusions already conceded and there is nothing to extract. You cannot be cross-examined out of a concession you already made honestly — so candor on direct is what survives a hostile cross. **23.** Any three of: **certainty** (created on the stand itself / over-claiming, the Mayfield trap — Ch. 14); **assumptions and inputs** (e.g., number of contributors, reconstructed temperature — the method's inputs, modeled on Ch. 13's dueling entomologists); **case-specific application** (the "reliable application" prong — Ch. 5); **contamination / chain of custody** (created at the scene and in handling — Ch. 2, Ch. 4); **bias / what you were told** (contextual bias — Ch. 31); **error rate and the literature** (the absence of a measured rate — Ch. 5, Ch. 6). (Acceptable to name the seam and its chapter; the point is that the vulnerability is created *upstream*, not in the science.) **24.** **Keep the verb on the evidence, never on the person's guilt.** "The evidence is consistent with…" / "strongly supports…" are safe; "the defendant is the source," "the chance he's innocent is…," "in my opinion he did it" are over the line. Holding that one line defeats overstatement, disarms the cross, and stays inside the ultimate-issue rule. **25.** **May say:** "The evidence is approximately a million times more probable if Mr. Keller contributed to this mixture than if an unknown, unrelated person did — very strong support for the first proposition over the second; it does not tell you he is guilty." **May not say:** "This is Mr. Keller's DNA" / "the probability he is innocent is one in a million." The forbidden sentence crosses the **transposed-conditional / prosecutor's-fallacy** line (and, by implying identity-as-proof, the **overstatement / ultimate-issue** line). Accept any honest "strength of support, with limits" sentence paired with any certainty/probability-of-guilt sentence correctly labeled. **26.** Because the step from "the evidence strongly supports that he was there / contributed" to "therefore he is guilty" is **the jury's step**, not the expert's — the **ultimate-issue rule** (§30.4). The jury must weigh *all* the evidence, the credibility of every witness, and the burden of proof, none of which is the expert's to assess. The experts supply the likelihood ratios and the findings at their true strength (the DNA "strongly supports / consistent with," the arson "incendiary on valid grounds") and *stop*; the jury supplies the prior and performs the final multiplication that yields a verdict.