B
Evidence Grade B
Graded
accuracy verified by the review judge
Safe to Cite
Recent
25%
25% -- effect size overestimation for Underpowered studies (2025)
Underpowered scientific studies routinely overestimate observed effect sizes by 25% to 50%.
- Reported as a range of 25-50%
- Based on a neuroscience meta-analysis applied by analogy to A/B testing
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Lighthouse Research Team
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Source verified
Evidence graded
Value
25%
Unit
Percentage
Data Vintage
2025
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
75
Source Trust
60
Citation Chain
20
Independence
30
Methodology
45
Freshness
95
Source
Nature Reviews Neuroscience
Primary
Tier B
https://kirro.io/ab-test-sample-size-formula ↗
Source Article
A/B Test Sample Size Formula, Explained With Examples
The A/B test sample size formula is:
n = (Zα/2 + Zβ)² × [p₁(1−p₁) + p₂(1−p₂)] / (p₁−p₂)²
If that looks like gibberish, you’re not alone. Most articles either throw this formula at you with zero explanation, or skip it and say “just use a calculator.”
This guide does both. We’ll break down every piec…
Original Research
Nature Reviews Neuroscience
· Original study ↗
Methodology
Range 25-50%; midpoint used; Nature Reviews Neuroscience study
Methodology documented
Segmentation
Industrymarketing
Cite this stat
Plain Text
Underpowered studies: 25% effect size overestimation. Source: Nature Reviews Neuroscience (2025). Via Lighthouse Intelligence -- https://lighthousedata.io/data/underpowered-studies-overestimate-25-50pct
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<blockquote cite="https://lighthousedata.io/data/underpowered-studies-overestimate-25-50pct" style="border-left:3px solid #2563eb;padding:12px 16px;margin:16px 0;font-family:system-ui,sans-serif;background:#f0f4ff;"><strong>25%</strong> -- effect size overestimation for Underpowered studies<br><small>Source: Nature Reviews Neuroscience (2025) · <a href="https://lighthousedata.io/data/underpowered-studies-overestimate-25-50pct" target="_blank" rel="noopener">Lighthouse Intelligence</a></small></blockquote>
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