Sample Size and Power

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Power is Affected by…..• Variation in the outcome (σ 2 )– ↓σ 2 → power ↑• Significance level (α)– ↑α →power ↑• Difference (effect) to be detected (δ)– ↑δ →power ↑• One-tailed vs. two-tailed tests– Power is greater in one-tailed tests than incomparable two-tailed tests
Power Changes• 2n = 32, 2 sample test, 81% power,δ=2, σ = 2, α = 0.05, 2-sided test• Variance/Standard deviation– σ: 2 → 1 Power: 81% → 99.99%– σ: 2 → 3 Power: 81% → 47%• Significance level (α)– α : 0.05 → 0.01 Power: 81% → 69%– α : 0.05 → 0.10 Power: 81% → 94%
Page 1 and 2: Sample Size and PowerLaura Lee John
Page 3 and 4: Take Away Message• Get some input
Page 5 and 6: Superiority vs. EquivalenceSuperior
Page 7 and 8: Vocabulary (2)• Follow-up period-
Page 9: Power Depends on Sample Size• Pow
Page 13 and 14: Power should be….?• Phase III:
Page 15 and 16: OutlinePower‣Basic Sample Size In
Page 17 and 18: Sample Size Formula Information•
Page 19 and 20: Sample Size & Study Design• Rando
Page 21 and 22: Take Away• Study’s primary outc
Page 23 and 24: Sample Size in Clinical Trials• T
Page 25 and 26: Phase I (Old Way)• Enroll 3 patie
Page 27 and 28: Phase IEnroll 3 people0/3 DLT 1/3 D
Page 33 and 34: Phase I (cont.)• Maximum Tolerate
Page 35 and 36: Phase I Note• *Implicitly targets
Page 37 and 38: Phase II Designs• Screening of ne
Page 39 and 40: Phase II Example:Two-Stage Optimal
Page 41 and 42: Two-Stage Optimal Design• Let α
Page 43 and 44: Blow up: Simon (1989) Table
Page 45 and 46: Phase II Example• If 4-10 of the
Page 47 and 48: Phase II• Newer methods are avail
Page 49 and 50: Phase II: Historical Controls• Ol
Page 51 and 52: Phase III Survival Example• Prima
Page 54 and 55: 341213
Page 57 and 58: Non-Survival Simple Sample Size•
Page 59 and 60: Sleep Aid Example• 1 sample test
Page 61 and 62:
Sample Size:Change Effect or Differ
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Sample Size: Change Power• Change
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Sleep Aid Example: 2 ArmsInvestigat
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Aside: 5 Arm Study• Sample size p
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Sample Size: Change Power• Change
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Conclusion• Changes in the differ
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Example• Calculate power with the
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JAVA Sample Size
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Move the Values Around• Sigma (st
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Keep Clicking “OK” Buttons
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Sample Size:Matched Pair Designs•
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Cohen's Effect Sizes• Large (.8),
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Take Home: N• Difference (effect)
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Unequal #s in Each Group• Ratio o
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Unequal #s in Each Group:Fixed # of
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# of Events is Important• Cohort
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# of Covariates and # of Subjects
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OutlinePowerBasic Sample Size Infor
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DNA Microarrays/Proteomics• Same
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Me, too! No, Please Justify N• "A
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Variance?• No prior information o
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OutlinePowerBasic Sample Size Infor
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No Estimate of the Variance?• Mak
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Top 10 Statistics Questions7. Each
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Top 10 Statistics Questions1. Repea
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Resources: General Books• Hulley
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Sample Size Specific Tables• Cont
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Resources: Articles• Schoenfeld,
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Resources: URLs• Sample size calc
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Sample Size and Power

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