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LNAT passages present a wide range of evidence to support their conclusions — from rigorous scientific studies to personal anecdotes, from government statistics to opinion surveys. Not all evidence is created equal. This lesson teaches you to evaluate the strength, reliability, and relevance of different types of evidence, a skill that underpins many LNAT Section A questions.
When evaluating any piece of evidence, consider three key dimensions:
| Dimension | Question to ask | What strong evidence looks like |
|---|---|---|
| Reliability | Can this evidence be trusted? | Large sample, rigorous methodology, independent source |
| Relevance | Does this evidence relate to the specific conclusion? | Directly addresses the claim, not tangentially related |
| Sufficiency | Is there enough evidence to support the conclusion? | Multiple independent sources, comprehensive data |
| Type | Example | Why it is strong |
|---|---|---|
| Large-scale randomised controlled trial | "A study of 10,000 patients found that Drug X reduced mortality by 20%" | Large sample, controlled methodology, quantifiable result |
| Official statistics from independent bodies | "ONS data shows that unemployment fell to 3.8% in Q3 2024" | Compiled by an independent, reputable organisation with established methodology |
| Systematic review or meta-analysis | "A meta-analysis of 45 studies confirms a link between air pollution and respiratory disease" | Aggregates evidence from multiple studies, reducing the impact of any single study's limitations |
| Replicated experimental findings | "The result has been replicated in laboratories across six countries" | Replication is the gold standard of scientific evidence |
| Type | Example | Why it is weak |
|---|---|---|
| Single anecdote | "My friend went to university and could not find a job, so degrees are worthless" | One case cannot establish a general pattern |
| Self-selected survey | "An online poll found that 90% of respondents oppose the policy" | Only people with strong views participate; not representative |
| Appeal to unnamed authority | "Experts say that this is the best approach" | Which experts? In what field? What is the basis for their claim? |
| Outdated data | "A 1985 study found that..." | Evidence from decades ago may not reflect current conditions |
| Evidence from a biased source | "Research funded by the tobacco industry found no link between smoking and cancer" | The funder has a financial interest in the outcome |
When a passage cites a scientific study, ask:
| Factor | Good survey | Poor survey |
|---|---|---|
| Sample | Random, representative | Self-selected, convenience |
| Size | Thousands of respondents | Dozens or hundreds |
| Questions | Neutral, unbiased wording | Leading or loaded questions |
| Response rate | High (>70%) | Low (<30%) |
| Conducted by | Independent research organisation | Organisation with a vested interest |
Expert opinion is valuable when:
Expert opinion is weak when:
"The policy worked in Sweden, so it will work here."
This type of evidence depends on the comparability of the two cases (see Analogical Reasoning in the companion course). Evaluate whether the contexts are sufficiently similar in the respects that matter.
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