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STAT 3743 Daily Outline

STAT 3743 Daily Outline

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2010-10-27 Wed

PANIC

If σ is unknown, use s instead

Remarks

– if pop'n normal then use Student's t critical value, get t-interval – if pop'n non-normal — if approx normal then still not too bad — if highly skewed or outliers, ask statistician

Example: SRS(7) from pop'n, assume norm, find CI for μ

Confidence intervals for difference of two means

intuition for the confidence interval

First suppose variances known: two-sample z-interval

If variances are unknown:

  • samples both large: use sample variances, approximate 100(1-α )% confidence
  • one (or both) samples small, then in trouble unless

– pop'ns both normal — if variances equal: pooled t-interval — variances unequal: Welch interval

Example: independent SRS(4) and SRS(7), norm

Author: G. Jay Kerns

Date: 2010-11-05 14:46:42 EDT

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