B
Evidence Grade B
Graded
accuracy verified by the review judge
Safe to Cite
Current
3%
3% -- share of tests picking fake winners with flat priors after one week for Bayesian A/B tests with flat priors (2026)
With flat priors, 3% or more of Bayesian A/B tests pick fake winners after one week.
- Source states '3%+', indicating at least 3%
Attribution:
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Lighthouse Research Team
Last verified:
·
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Source verified
Evidence graded
Value
3%
Unit
Percentage
Data Vintage
2026
Entity
Evidence Quality
B
Strong, reliable evidence
Sourced from a well-regarded research firm or industry leader with transparent methodology and a reasonably large sample.
Single source - not yet corroborated
Score breakdown
Extraction
50
Source Trust
60
Citation Chain
20
Independence
30
Methodology
45
Freshness
95
Source
Andrew Gelman
Primary
Tier C
https://kirro.io/bayesian-ab-testing ↗
Source Article
Bayesian A/B testing: when it helps (and when it doesn't)
Bayesian A/B testing measures which version of a page works better using a probability that updates as data comes in. Instead of waiting for some magic number of visitors, you get a running answer: “Version B has an 89% chance of getting more signups.”
That’s it. No statistics degree required.
Peopl…
Original Research
Andrew Gelman
· Original study ↗
Methodology
Attributed to statistician Andrew Gelman's warning on flat priors
Methodology documented
Segmentation
Industrymarketing
Cite this stat
Plain Text
Bayesian A/B tests with flat priors: 3% share of tests picking fake winners with flat priors after one week. Source: Andrew Gelman (2026). Via Lighthouse Intelligence -- https://lighthousedata.io/data/gelman-flat-prior-fake-winners-3pct
HTML Embed
<blockquote cite="https://lighthousedata.io/data/gelman-flat-prior-fake-winners-3pct" style="border-left:3px solid #2563eb;padding:12px 16px;margin:16px 0;font-family:system-ui,sans-serif;background:#f0f4ff;"><strong>3%</strong> -- share of tests picking fake winners with flat priors after one week for Bayesian A/B tests with flat priors<br><small>Source: Andrew Gelman (2026) · <a href="https://lighthousedata.io/data/gelman-flat-prior-fake-winners-3pct" target="_blank" rel="noopener">Lighthouse Intelligence</a></small></blockquote>
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