B
Evidence Grade B
Graded
accuracy verified by the review judge
Safe to Cite
Current
30%
30% -- false winner rate for A/B testers peeking at every 10% of sample (2026)
Checking A/B test results at every 10% of the sample leads to picking fake winners 30% of the time.
Attribution:
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Lighthouse Research Team
Last verified:
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Source verified
Evidence graded
Value
30%
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
CXL
Primary
Tier C
https://kirro.io/a-b-testing-mistakes ↗
Source Article
11 A/B testing mistakes (and how to avoid them)
You’re running A/B tests. That already puts you ahead of most websites. But running tests and running them well are two different things.
Bad tests are worse than no tests. They give you confidence in the wrong answer. You make changes based on data that looked real but wasn’t. Then conversions drop…
Original Research
CXL
· Original study ↗
Methodology
CXL research on peeking, cited by Kirro
Methodology documented
Segmentation
Industrymarketing
Cite this stat
Plain Text
A/B testers peeking at every 10% of sample: 30% false winner rate. Source: CXL (2026). Via Lighthouse Intelligence -- https://lighthousedata.io/data/peeking-every-10pct-fake-winners-30pct
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<blockquote cite="https://lighthousedata.io/data/peeking-every-10pct-fake-winners-30pct" style="border-left:3px solid #2563eb;padding:12px 16px;margin:16px 0;font-family:system-ui,sans-serif;background:#f0f4ff;"><strong>30%</strong> -- false winner rate for A/B testers peeking at every 10% of sample<br><small>Source: CXL (2026) · <a href="https://lighthousedata.io/data/peeking-every-10pct-fake-winners-30pct" target="_blank" rel="noopener">Lighthouse Intelligence</a></small></blockquote>
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