CPR APPLICATIONS FOUNDATION · CHAPTER 20 · TREATMENT
Treatment Foundations of Biostatistics & Epidemiology
Organize the chapter before drilling into individual CPR concepts.
Supplemental foundation map: this page orients the detailed CPR Applications for Chapter 20. It is not part of the canonical CPR object inventory.
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Normal Foundations
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Treatment Foundations · You are here
20.25 · SOURCE CPR FOUNDATION
Concept
Evidence-based decisions turn test results and study findings into action. The best decision depends on baseline risk, test performance, effect size, harms, cost, patient values, and population impact. Step 1 often asks what decision the data support, not whether the data look impressive.
Pattern
Step 1 gives an intervention with benefit and harm, a diagnostic test with tradeoffs, a screening program, or a public-health scenario. The correct response often uses absolute risk, NNT, NNH, pretest probability, or reporting obligations to choose the safest next step.
Rule
- Use absolute benefit for clinical decisions. Relative benefit alone can mislead.
- Use test results to change management only when they change probability enough. Testing without decision impact creates harm.
- Use population metrics for public-health decisions. Outbreaks and vaccination require group-level thinking.
Applications
- Low-prevalence setting with positive screening test → review positive predictive value and pursue appropriate confirmation rather than assuming disease
- High-risk patient negative weak test → further evaluation may still be needed
- Treatment with small ARR and serious harms → caution
- Vaccine outbreak scenario → population-level prevention
- Patient counseling → communicate absolute risk
- Tip: Evidence matters most when it changes a decision
CPR APPLICATIONS · ACTIVE REASONING
Turn evidence into a defensible clinical decision
Commit to an answer before requesting feedback. Full worked explanations remain available if scripts are unavailable. Answers are not transmitted or stored.
Reveal the worked answer and changed-variable challenge
Best answer: 50. The absolute risk reduction is 0.04 − 0.02 = 0.02; NNT = 1/0.02 = 50 over the stated time horizon.
Transfer: If baseline risk rises to 20% and risk falls to 10% with the same relative reduction, how does NNT change?
Reveal the worked answer and changed-variable challenge
Best answer: Post-test probability may remain high enough to justify additional evaluation. Interpret negative results using pretest probability, likelihood ratios, disease consequences, and available testing.
Transfer: What would change if the test had very high sensitivity and a sufficiently low negative likelihood ratio?
Reveal the worked answer and changed-variable challenge
Best answer: Absolute benefit, harm likelihood, uncertainty, and patient priorities. NNT/NNH, risk context, clinical importance, and patient values determine whether treatment is worth its cost and harm.
Transfer: How could the balance change for a patient at much higher baseline risk?
Change the mechanism
Read all comparisons without scripts
- Event risk 4% → 2%: ARR 2 percentage points; NNT = 50 over the period studied.
- Event risk 20% → 10%: ARR 10 percentage points; NNT = 10 over the same period.
- Test negative with high pretest probability: The result may not reduce post-test probability below the management threshold.
Explain it back: Identify the mechanism, name the most important competing explanation, and predict what changes when the context shifts.
Unscored educational reasoning. Not a validated assessment or individualized clinical recommendation.
How to use this foundation map
- Identify the organizing mechanism.
- Recognize the pattern.
- Restate the rule without looking.
- Test transfer with applications and question practice.
Pair CPR with the 5P Approach™ when solving cases and questions.