Chapter 6 Exercises

Work these in order; they climb from recall to applied reasoning to ethics. Items marked with a dagger (†) have worked solutions in the answers appendix — try them before you look. No answers are given in this file.

A. Recall and definitions

  1. Define wrongful conviction in a single precise sentence, making clear how it differs from a conviction reversed for a procedural error.

  2. Define exoneration. Name the three legal mechanisms by which an exoneration commonly occurs.

  3. † In your own words, define junk science and explain why an honest examiner can be the vehicle for it. Use a one-sentence example.

  4. Who founded the Innocence Project, in what year, and what was its core operating model?

  5. State, from memory, the central finding of the 2009 NAS report in one sentence (paraphrase is fine).

  6. The 2009 NAS report called American forensic science "______." Fill in the two-word phrase and explain what it meant.

  7. Define foundational validity as the PCAST 2016 report uses it, and distinguish it from validity as applied.

  8. What is a black-box study, and what does it measure?

  9. List the leading contributing causes of wrongful conviction revealed by the DNA exonerations, in rough order of how often they appear.

  10. † State the three rules for using the validity spectrum given in §6.6.

B. Applied reasoning

  1. A method has never been the subject of a black-box study, but it has been used in tens of thousands of real cases over fifty years with "no known errors." A prosecutor argues that this track record is validation. Refute the argument using the pilot-who-never-learns analogy.

  2. † Explain why DNA was uniquely able to produce exonerations when no prior forensic technology had done so at scale. Name the two properties that made it possible.

  3. Roughly half of the DNA exonerations involved "flawed or misapplied forensic science." Distinguish the two sub-categories that phrase contains, and give an example method for each.

  4. The same forensic discipline can sit at opposite ends of the validity spectrum. Choose one (not odontology, which the chapter uses) and give two claims — one the science supports, one it does not.

  5. After PCAST 2016, an examiner may testify to a latent-print match. Write the one additional thing PCAST says the examiner must include, and write a sentence of courtroom testimony that complies.

  6. † A detective tells the lab analyst, before analysis, "We're sure it's the boyfriend — just confirm the print is his." Identify the bias risk this creates and name the safeguard (forward-referencing the chapter that develops it).

  7. Why are the countable DNA exonerations a biased sample of all wrongful convictions? What kind of case is systematically missing from the count, and why?

  8. The chapter argues that the causes of wrongful conviction "interlock." Walk through one concrete cascade: start with a mistaken eyewitness ID and end with a hardened case against an innocent person, naming each link.

C. Evidence interpretation and "spot the overstatement"

  1. † An examiner testifies: "Fingerprint identification has a zero error rate; this print is the defendant's, to the exclusion of all others on Earth." Identify every overstatement in this sentence and rewrite it as defensible testimony.

  2. A serologist's report on a real, valid blood-typing method states a conclusion the underlying data do not support. Is this junk science, fraud, or overstated valid science? Justify your classification.

  3. Read this claim: "Bite-mark comparison is admissible in many courts, so it must be scientifically valid." Name the two distinct errors in the reasoning (one historical/legal, one about what admissibility measures).

  4. † A method's central claim is "I can match this mark to one unique source by visual comparison," and no published study measures how often that matching is wrong. Apply the chapter's "tell" for junk science and state your verdict and your reasoning.

  5. An examiner from a foundationally valid discipline reports a result without stating the error rate from the validation studies, instead using the phrase "to a reasonable degree of scientific certainty." Which report's recommendation does this violate, and what should the testimony have said?

  6. Rank these four statements about a single comparison from strongest claim to weakest claim, and say which the science most often supports: (a) "is consistent with"; (b) "identifies, to the exclusion of all others"; (c) "cannot be excluded"; (d) "strongly supports, with a stated probability."

D. Ethics and judgment

  1. † You are a lab analyst. A method your lab routinely uses was, after PCAST 2016, found to lack established foundational validity for the specific claim your reports make. Your supervisor says to keep reporting as before because "the courts still accept it." Lay out your ethical obligations and your options. (Connect to Chapter 5 admissibility and forward to Chapter 38 ethics.)

  2. Is it ethical for a prosecutor's office to oppose post-conviction DNA testing on the basis of "finality" when the evidence is preserved and the test is inexpensive? Argue both sides, then state your own position and your reasoning.

  3. A juror writes after a trial: "There was no DNA, so I had reasonable doubt and voted to acquit." Discuss how this reflects the CSI effect, and whether the juror's reasoning was sound or unsound in this instance (note: you cannot tell from the statement alone — explain why).

  4. The chapter says junk science is "worse in a way" than fraud. Construct the strongest argument against that claim — i.e., why fraud might be the greater danger — and then respond to it.

  5. An examiner sincerely believes in a method the science has discredited and testifies in complete good faith. Where, if anywhere, does moral responsibility lie for a resulting wrongful conviction — with the examiner, the discipline, the court that admitted it, or the system? Defend a position.

  6. † Write the single most important standing instruction a forensic scientist should give themselves to avoid contributing to a wrongful conviction. Justify your choice in three sentences, drawing on at least two of the book's four themes.

E. Cold-case extension

  1. † Reopen the Mill Creek file. List the warning signs in the Cody Renner confession that the exoneration literature would flag as dangerous, and explain — using the bias cascade — how the early "accidental fire" narrative and the later focus on a convenient local could reinforce each other.

  2. The chapter instructs you to log a standing instruction in the case file: the evidence must be allowed to exclude Renner if it can. Explain why this is a methodological commitment and not a statement that Renner is innocent. What future evidence (name the chapters) would be capable of excluding him?

  3. A detective on the cold case argues, "We have a signed confession — the forensic stuff is just confirmation." Using this chapter, explain precisely what is wrong with treating a confession as the fixed point against which evidence is merely confirmed.

  4. Suppose, hypothetically, that a careless examiner later reported a hair from the cabin as a "match" to Renner. Trace how that single overstatement could have combined with the confession to produce a wrongful conviction — and identify every point in the chain where an honest practice would have broken it.

  5. Map the Mill Creek case's current risk profile onto the leading-causes table from §6.3. Which causes are present or possible at this stage, and which are not yet in play? What does that tell you about where the danger is highest right now?