Chapter 1 Exercises

Work these with the chapter's habits of mind: name the class-vs-individual distinction, choose the honest verb (exclude / consistent with / strongly supports), and refuse to claim more than the evidence bears. Items marked † have worked solutions in Appendix: Answers to Selected Exercises. There are no answers in this file — attempt every one before checking.

A. Recall and definitions

  1. † In one sentence each, define forensic science and criminalistics, and state how they differ.
  2. What does the Latin root forum tell you about why forensic work is performed under conditions ordinary science is not?
  3. List four forensic specialties from the chapter that operate largely outside the criminalistics lab.
  4. † Define class characteristic and individual characteristic, and give one original example of each (not the shoe example from the text).
  5. State, in your own words, what it means to individualize a piece of evidence, and why the claim is problematic outside of quantified DNA.
  6. What two reports furnish the book's "validity spectrum," and what year is each from?
  7. Name the book's four recurring themes.

B. Apply the class/individual distinction

  1. For each item, say whether the described feature is a class or an individual characteristic, and why: (a) a tire impression showing a particular tread design; (b) a tire impression showing a specific gouge from a nail embedded in one tire; (c) blood typed as O-positive; (d) a full 20-locus DNA profile; (e) a torn edge of paper that fits one notepad jigsaw-fashion.
  2. † A jacket fiber at a scene is "consistent with" fibers from a suspect's jacket: same color, same polyester composition, same cross-section. Which end of the class→individual arrow is this, and what would it take to move it toward the other end?
  3. Explain why "the suspect and the shoe impression are both size 11" can be true and nearly useless at the same time.
  4. Rank these associations from weakest to strongest and justify the order: (a) same ABO blood type; (b) consistent microscopic hair appearance; (c) a single-source DNA profile agreeing at 20 loci; (d) a physical (fracture) match of two broken pieces.

C. Choose the honest verb

  1. † Rewrite each overstated sentence so it claims only what the chapter says is defensible: (a) "The print proves the defendant touched the weapon." (b) "The hairs are a match, so they are the defendant's." (c) "These teeth made this bite mark to a reasonable degree of scientific certainty."
  2. A lab reports that a suspect "cannot be excluded" as a contributor to a sample. A newspaper headline reports the suspect "linked by DNA." Explain precisely what the headline gets wrong.
  3. Give an example, in any discipline, where a single honest disagreement between evidence and a suspect should end the inquiry into that suspect.

D. The CSI effect and validity spectrum

  1. Describe the two opposite ways the CSI effect can distort a jury's verdict, with a concrete scenario for each.
  2. † A defense attorney says, "There was no DNA, no fingerprints — the state has nothing." Using the chapter, give two reasons this argument can be misleading even when it is literally true.
  3. Using the validity-spectrum table (§1.5), explain why forensic odontology can appear in both a "reliable" and an "unreliable" sentence without contradiction.
  4. Why is "the method has a known, published error rate" a good sign about a discipline rather than a damaging admission?

E. Reasoning and judgment

  1. † A method claims to match a mark to a single unique source by visual comparison and has no published studies measuring how often that match is wrong. What is the single most important question to ask about it, and why does its absence amount to a finding?
  2. Forensic science is described as excluding more reliably than it proves. Construct an example (real or invented) in which exclusion is the most valuable thing the lab does in a case.
  3. Explain the difference between cynicism and calibration as responses to the CSI effect, and why the book argues for the second.
  4. Why does a discipline that "cannot imagine being wrong" tend to never measure how often it is? Tie your answer to at least one theme.

F. Ethics and communication

  1. You are an analyst whose true result is "consistent with, cannot exclude." The prosecutor asks you to testify that it's "a match." List three distinct problems with agreeing, drawing on the chapter.
  2. † Draft two sentences you could say on the witness stand that convey a fingerprint association honestly — one that a competent cross-examiner could not fairly call an overstatement.
  3. Why is "clearing the innocent" described as potentially forensic science's "finest hour" rather than a secondary function?

G. The Cold Case

  1. Write the one-sentence question at the top of the Mill Creek case file, exactly as §1.7 frames it.
  2. † The first report assumes an accidental fire. Name the cognitive trap in treating that first, reasonable assumption as the conclusion to be confirmed, and state the methodological correction the chapter prescribes.
  3. List three kinds of evidence you already expect the later chapters to add to the file, and for each, write the honest verb you would want the eventual result to use rather than "proves."