Separate the observation, the source, and the inference. A precise number is useful only if its provenance, scope, and limitations are clear.
For each consequential claim, record the source, the comparison group, the uncertainty, and the decision it is being used to support.
How It Works
Effective use of evidence requires more than dropping statistics into an argument. The evidence must be relevant, specific, and presented in a way that the audience can process quickly. A single well-chosen number often outperforms a barrage of data points. The technique works best when the evidence is surprising or counterintuitive, because it forces the audience to update their mental model. A debater who says "studies show" without specifying which study, from which institution, with what sample size, weakens rather than strengthens their position.
Evidence and explanation serve different roles. An observed change after a policy does not, on its own, establish that the policy caused it. State the proposed mechanism, examine alternative explanations, and use an appropriate comparison before making a causal claim.
When to Use It
Appeal to evidence is essential in policy debates, scientific discussions, and any context where the audience values objectivity. It is the dominant technique in academic settings, courtroom proceedings, and policy advocacy. It works particularly well against opponents who rely on anecdote or emotion, because it forces the debate onto factual terrain where subjective impressions carry less weight.
The technique has limitations. Against an audience that distrusts the sources of evidence (institutions, experts, mainstream research), it can backfire. Evidence also struggles against well-constructed narratives; a single compelling story often outweighs a stack of statistics in the minds of most listeners. The most effective debaters pair evidence with narrative, using data to anchor a story rather than replacing it.