week 5 - confidence intervals and effect size

• confidence intervals allow us to ...

  measure uncertainty about estimates, describes a range of values within which the true population parameter should occur
• what is an effect size

  standard way to quantify effect
• 95% of z-scores are found between

  -1.96 and +1.96
• critical values of percentages in CIs only work when

  • using mean distributions
  • large numbers of samples (>30)
• When n<30 what do we use instead

  t-distributions as they are slightly broader with lower values of n so CI would be wider which accounts for uncertainty caused by smaller samples
• what is the relationship between CI and sample size


  CI decreases and sample size increases
• What are equations for CI

  • mean +/- 1.96 x SEM
  • point estimate +/- critical value x standard error
  • mean +/- critical value of t x SEM