t-test and SD vs SE (SEM)

t-test

• t-test on Wiki for 2 samples
  • equal sample size N, equal variance
    • variance: standard deviation (SD) of population
  • equal variance, UNequal size
  • UNequal variance
• assumptions & unbalance
  • example 1 - unequal variance may be informative itself !
  • example 2
  • details of assumption violation

SD vs SE(SEM) – deviation vs error

• SD: standard deviation, wiki link
• SE: standard error (of sampling distibution of an statistic, e.g. mean, then is SEM - SE of Mean), wiki link
• SD vs SEM
  • sem = sd/sqrt(n)
  • more
• SEM: good explanation figures