confidence interval

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Note

  • confidence level
    • alpha risk = 1 - confidence level, the risk that population parameter (e.g. mean) is not within the CI
    • confidence LEVEL up WIDER confidence interval less practicall value
    • confidence level 68% t-stats ~= 1 (from the T-table)
    • confidence level 95% t-stats ~= 2
    • confidence level 99% t-stats ~= 3
  • CI(mu) = sample mean +- MOE = sample mean +- Tstats * SEmean
    • CI = 2*MOE
  • Sample size n
    o   sample size n up narrower confidence interval (by sqrt(n))
    o   at n = 25, reduction of 80% of CI is achieved
    o   if n<30, sample mean is a student-distribution and t-stats needs to be defined from the Z-table

Resources


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