Chapter 10 — Self-Check Quiz

24 questions: multiple choice and short answer. Try them closed-book, then check the key at the bottom. The goal is calibration — not just the right answer, but knowing why the wrong answers are wrong.

Multiple choice

  1. Serology is best defined as: - A. The reconstruction of events from bloodstain geometry - B. The forensic identification and characterization of blood and other body fluids - C. The statistical interpretation of DNA mixtures - D. The study of insect activity on remains

  2. A presumptive test for blood is characterized by being: - A. Highly specific and slow - B. Sensitive and fast, but capable of false positives - C. The final word on whether a stain is human blood - D. Unable to produce a meaningful negative result

  3. A Kastle-Meyer test produces which color when positive? - A. Blue-green - B. A blue glow visible only in darkness - C. Pink - D. Brown

  4. Every common presumptive blood test actually detects: - A. Human-specific antigens - B. Nuclear DNA - C. The peroxidase-like activity of the heme group - D. Red blood cell nuclei

  5. Which is a documented luminol false positive? - A. Saliva - B. Bleach / oxidizing cleaners - C. Distilled water - D. Cotton fabric

  6. A free-falling drop of blood in flight takes the shape of: - A. A teardrop - B. A flattened disc - C. A sphere - D. An ellipse

  7. The angle of impact of a bloodstain is estimated from: - A. The color of the stain - B. The ratio of the stain's width to its length - C. The total number of stains in the pattern - D. The distance to the nearest wall

  8. A long, narrow elliptical stain with a small tail indicates: - A. A drop that struck at a near-90° (overhead) angle - B. A drop that struck at a shallow (glancing) angle, traveling toward the tail - C. A passive drip - D. That the blood is non-human

  9. Spatter correctly refers to: - A. Blood projected through the air as droplets by an applied force - B. A pool of blood formed by gravity - C. Any stain confirmed to be impact-caused - D. A transfer pattern from a bloody hand

  10. The area of origin reconstruction produces:

    • A. A precise three-dimensional coordinate
    • B. The identity of the weapon
    • C. A bounded three-dimensional region with real uncertainty
    • D. The sequence of blows

  11. The straight-line "stringing" method tends to place the area of origin:

    • A. Too low, because it overcorrects for gravity
    • B. Too high, because it ignores the droplet's parabolic (gravity-curved) path
    • C. Exactly correct, because blood travels in straight lines
    • D. In a random location

  12. The 2009 NAS report's assessment of bloodstain pattern analysis was that:

    • A. It is the gold standard of forensic reconstruction
    • B. Its interpretations are often more subjective than scientific, with large uncertainties
    • C. It should never be used in any form
    • D. It is fully validated with a known error rate

  13. The single best DNA source listed among these, and the rule for packaging it, is:

    • A. Blood; seal it wet in plastic to preserve moisture
    • B. Blood; air-dry and package in breathable paper
    • C. Red blood cells specifically, because they are nucleated
    • D. Luminol residue; refrigerate in a sealed jar

  14. After serology confirms a stain is human blood, the question "whose is it?" is answered by:

    • A. A second Kastle-Meyer test
    • B. The area-of-origin reconstruction
    • C. DNA analysis (Chapters 7–9)
    • D. The precipitin test alone

  15. The David Camm case is used in this chapter to illustrate:

    • A. A luminol false positive
    • B. That qualified BPA experts examining the same stains reached opposite conclusions
    • C. The reliability of impact-angle measurement
    • D. A successful single-source DNA match

  16. A presumptive blood test's negative result is valuable because:

    • A. It confirms the stain is human
    • B. It is a reliable exclusion — detectable blood is not present
    • C. It identifies the source
    • D. It establishes the time of deposition

  17. The most defensible single measurement in BPA is:

    • A. The number of blows
    • B. The handedness of the assailant
    • C. The directionality and impact angle of individual stains
    • D. The exact time the spatter was created

  18. Which testimony is defensible?

    • A. "The blood proves the defendant beat the victim."
    • B. "The area of origin is roughly 30–50 cm above the floor, with substantial uncertainty."
    • C. "I can read the entire attack from the spatter, blow by blow."
    • D. "Luminol glowed, so the room was the murder scene."

Short answer

  1. In one sentence each, state what serology establishes and what only DNA can establish about a bloodstain.

  2. Name the two-stage funnel of serology and explain why a presumptive positive never ends the inquiry.

  3. Give two reasons luminol must be used thoughtfully even though it can reveal cleaned-up blood (name a downstream-evidence cost and a specificity cost).

  4. Explain why "spatter is present" cannot, by itself, tell you what event produced it.

  5. A BPA analyst is told the detective's theory before interpreting the stains. Name the bias hazard and the safeguard, and explain why the resulting opinion is compromised even if correct.

  6. State, in courtroom-ready language, the most a careful BPA analyst may honestly say — and one thing they must never say.

Answer key (click to expand) **Multiple choice** 1. **B** — serology is the identification/characterization of body fluids. (A) is BPA; (C) is DNA statistics; (D) is entomology. 2. **B** — fast and sensitive, but false-positive-prone; its *negative* is reliable, so (D) is wrong. 3. **C** — pink (phenolphthalein). (A) is leucomalachite green; (B) is luminol. 4. **C** — heme's peroxidase-like activity, which is exactly why non-blood peroxidases (e.g., horseradish) fool it. 5. **B** — bleach/oxidizing cleaners are a classic luminol false positive (also metal ions, plant peroxidases, rust). 6. **C** — surface tension pulls an airborne drop into a sphere; the "teardrop" is a myth. 7. **B** — width-to-length ratio; $\sin(\text{angle}) = \text{width}/\text{length}$. 8. **B** — shallow angle, traveling toward the tail/narrow end. 9. **A** — projected droplets dispersed by a force; it is a physical description, not a cause. 10. **C** — a bounded region with uncertainty, never a precise point or the weapon/sequence. 11. **B** — it ignores the parabolic, gravity-curved path, placing the origin too high. 12. **B** — the NAS found BPA interpretations often more subjective than scientific, with enormous uncertainties. 13. **B** — blood, air-dried and packaged breathable; plastic traps moisture and ruins DNA. (Red cells are *not* nucleated, so C is wrong.) 14. **C** — DNA answers "whose." 15. **B** — Camm: opposite expert conclusions on the same shirt stains. 16. **B** — a clean negative is a reliable exclusion (Theme 1). 17. **C** — directionality and impact angle are the defensible measurements. 18. **B** — modest, uncertainty-stated geometry; the others narrate or overstate. **Short answer (model points)** 19. *Serology:* that a biological fluid is present and which one it is (e.g., human blood). *DNA:* whose it is (source attribution, with a probability). 20. Presumptive (fast, sensitive, screening) → confirmatory (specific, identifying) → then DNA. A presumptive positive says only "could be — keep going," because non-target substances can trigger it; identification requires the confirmatory step. 21. (1) Downstream cost: luminol and its alkaline conditions can *degrade DNA*, harming later typing. (2) Specificity cost: it is *presumptive*, glowing for bleach, metal ions, and plant peroxidases, so a glow is a question, not an identification. 22. The same general field of dispersed droplets can arise from different mechanisms (impact, arterial breach, cast-off, expirated). "Spatter" describes the droplets' physical state; choosing the *cause* is an interpretive inference the geometry alone cannot make. 23. Hazard: **contextual bias** (expectation steering a subjective interpretation). Safeguard: **context management / blind analysis** — keep the analyst unaware of the desired conclusion and measure the stains' features first. The opinion is compromised because we can no longer tell whether the analyst *saw* the conclusion in the blood or *brought* it to the blood; a correct-by-luck opinion produced under bias still lacks reliability. 24. *May say:* identify clear pattern categories; state directionality; estimate impact angles and an area-of-origin region with explicit uncertainty; say an account is *consistent with* or *difficult to reconcile with* the pattern. *Must never say:* a blow-by-blow narration of the crime, a precise origin point, a single mechanism to the exclusion of others without basis, or any of it "to a reasonable degree of scientific certainty" as if it were measured.