Evaluating Evidence and Sources

Not all evidence carries the same weight

When evaluating a claim, “there’s evidence for it” isn’t enough on its own. You need to check whether the evidence is relevant, sufficient, accurate, and able to rule out other explanations. Personal experience, expert opinion, statistics, and experimental results each have different strengths and limits.

Critical thinking isn’t about dismissing evidence — it’s about telling strong evidence from weak evidence.

Standards for evaluating evidence

Standard	Question to ask
Relevance	Does this material actually connect to the claim?
Sufficiency	Are there too few examples?
Accuracy	Do the numbers and quotes match the original?
Representativeness	Is a partial sample being treated as the whole?
Currency	Is this information still applicable now?

You can’t check every one of these standards perfectly every time, but the more important the decision, the more of them you should check.

The basics of source criticism

When looking at a source, check who is saying it, what interests they might have, whether primary data exists, and whether they treat opposing views fairly. Blog posts and videos can be useful, but you still need to check the original data and evidentiary structure behind them.

Be especially careful with the phrase “studies show.” Without checking which study, who the sample was, and whether the conclusion actually says what’s claimed, that phrase can just be borrowing the tone of authority.

Example: judging general information, not a supplement ad

“A lot of people saw results” might be an anecdote, but it isn’t necessarily sufficient evidence. Conditions vary from person to person, and it’s possible only the people who saw results bothered to leave a review. In cases like this, look at the comparison standard, the measurement method, and whether side effects are mentioned.

Key takeaways

• “There’s evidence” isn’t enough — you have to look at the quality of the evidence.
• Relevance, sufficiency, accuracy, representativeness, and currency are the basic evaluation standards.
• Check a source’s interests and whether primary data exists.
• Even phrases like “studies show” need their actual evidentiary structure checked.

Next chapter: the traps of causal reasoning — one of the most common sources of confusion when weighing evidence.