A Practical Checklist for Evaluating Everyday Claims

Critical Thinking

Chapter 9 · A Practical Checklist for Evaluating Everyday Claims

Eight chapters, eight techniques — this chapter compresses all of them into one practical checklist, then runs a real, current claim through it to show what an honest answer actually looks like.

The Checklist

#	Check	From
1	Break the claim into smaller, checkable parts	Chapter 1 — Fermi-izing
2	Check how it's argued, not just what it concludes	Chapter 2 — Fallacies
3	Notice your own reaction before trusting it	Chapter 3 — Cognitive biases
4	Ask whether it's actually causal, or just correlated	Chapter 4 — Correlation vs. causation
5	Check the real base rate behind any percentage	Chapter 5 — Statistical traps
6	Ask whether repetition or a named device is doing the persuading	Chapter 6 — Propaganda
7	Reframe it the opposite way and see if your reaction changes	Chapter 7 — Framing
8	Ask whether consensus reflects evidence or social pressure	Chapter 8 — Groupthink

A Real, Compact Worked Example

Claim: "Vitamin C prevents colds." Applying steps 1, 4, and 5 — breaking it down, checking causation, and checking the real base numbers:

Hemilä & Chalmers, Cochrane Review

Across 29 trial comparisons and over 11,000 participants in the general population, regular vitamin C supplementation showed no meaningful effect on how often people caught colds (risk ratio 0.97 — close to no effect). But in five trials covering 598 people under intense physical stress (marathon runners, skiers, soldiers in subarctic conditions), the real risk ratio was 0.48 — a genuine, substantial reduction. Separately, regular supplementation modestly reduced cold duration once someone was already sick — by about 8% in adults and 14% in children.

The Honest Answer

"Does vitamin C prevent colds?" doesn't have a clean yes-or-no answer, and the checklist is exactly what surfaces that: no, for most people, regular supplementation doesn't meaningfully prevent catching a cold — but yes, for people under real physical extremes, and yes, it modestly shortens a cold's real duration once you have one. Most everyday claims that survive this checklist end up looking like this — genuinely true under some conditions and false under others, not simply right or wrong.

Hands-On Exercises

Exercise 1

Pick a real health, productivity, or news claim you've encountered recently. Apply checklist items 1, 4, and 5 specifically — breaking it down, checking for causation, and checking the real base rate — and report what you find.

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Exercise 2

Explain, in your own words, why "vitamin C prevents colds" being false for the general population but true for people under physical stress is a genuinely different kind of finding than the claim simply being wrong.

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Exercise 3

Explain, in your own words, why running through all eight checklist items on every single everyday claim you encounter would be impractical, and propose a real, reasonable rule for deciding when a claim actually deserves the full checklist versus a quicker gut check.

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Chapter 9 Quick Reference

The eight-item checklist maps directly onto each of the course's own prior eight chapters
A real Cochrane review found vitamin C has no meaningful effect on cold incidence in the general population (risk ratio 0.97)
But it shows a real, substantial effect under intense physical stress (risk ratio 0.48) and modestly reduces cold duration (8% adults, 14% children)
Most everyday claims that survive real scrutiny end up conditionally true, not simply right or wrong