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Illusory truth effect and repeated claims in event markets

Hear a claim often enough and it starts to feel true. Psychologists have studied this for nearly five decades and call it the illusory truth effect. In event markets, where rumours, talking points and confident commentary circulate quickly, repetition can move prices before anyone checks whether the claim has a real source. This SoftCta guide explains the effect and practical defences.

The research

In 1977, Lynn Hasher, David Goldstein and Thomas Toppino showed participants a series of plausible statements over several sessions. Statements that were repeated were rated as more likely to be true than new ones, regardless of whether they were actually true. Later work found the effect across many kinds of claims. Research led by Lisa Fazio found that repetition can increase belief even in statements that contradict what people already know, although knowledge reduces the effect.

Why repetition persuades

A leading explanation is processing fluency. A statement we have encountered before is easier to process, and that ease feels like a sign of truth. In everyday life, repeated information often is true, so the shortcut works. It fails when false or unverified claims are repeated widely.

Where it shows up in event markets

• Rumours: a report that a deal is close or a candidate will withdraw can be reposted many times, as discussed in our guide on how rumours move prices.
• Market comments: the same view repeated by several commenters can feel like consensus; see reading comments without herding.
• Commentary: talking points repeated across outlets can create a narrative that outruns evidence, as in our narrative fallacy guide.
• Cascades: traders who buy because others did can reinforce the claim's apparent credibility, discussed in information cascades.

Count sources, not repetitions

Ten posts quoting the same anonymous account are one source, not ten. When you see a claim, trace it back. Who first said it? Do they have direct knowledge? Has an official body confirmed it? Our guide on primary sources versus headlines explains why the original document matters more than the volume of coverage.

Habits that help

• Note the first time you saw a claim and its original source.
• Ask what evidence would confirm or refute it, and whether that evidence exists yet.
• Separate what you know from what you have heard.
• Pause before reacting to a price move driven by a repeated claim. Our odds move primer helps frame how much a price has moved.

A reading habit

When a claim feels obviously true, ask whether that feeling comes from evidence or familiarity. Check the market's named settlement source, compare your estimate with the price, and verify live prices on the venue before acting.

Primary sources SoftCta readers open

• Hasher, Goldstein and Toppino's 1977 study on frequency and validity
• Fazio and colleagues' research on knowledge and illusory truth
• Official primary sources named in each market's rules
• Fact-checking organisations' published methods

Reading the quote step by step

• Read the full title and rules, including the named settlement source and the time zone.
• Convert the Yes and No prices to implied probabilities and note the gap between them.
• Subtract fees and spread to see the effective price you would actually face.
• Write your own probability range and the evidence behind it, then compare.
• Check related and near-duplicate markets on other venues for consistency.

Closing SoftCta checklist

• Re-read the venue definition in your own words before reacting to a price.
• Convert prices with fee and spread awareness; verify live cents on the operator.
• Prefer primary settlement sources over secondary headlines and social summaries.
• Treat ChanceWire hubs, movers, and tools as orientation — not order entry.
• Confirm age, location, and product eligibility; SoftCta pages will not suggest location spoofing.
• If clarity is incomplete, watching is a complete SoftCta outcome — no pick-selling urgency required.

SoftCta habits

• Write your own probability range before checking the crowd price.
• Prefer dated primary sources over social summaries.
• Compare related markets when a single book looks extreme.
• Size curiosity with fees and depth in mind; substantial risk of loss.