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Analysis of Variance (ANOVA)



Analysis of Variance - Hypothesis test used to evaluate mean differences between more than
two groups



Problems with multiple t tests - Unacceptably high probability of Type I Error (alpha), also
called alpha inflation



Variance - a measure of variability = standard deviation squared



Two source of variance - 1. Between group variance

2. Within group variance



Between group Variance - Between group means, cause by independent variable + some
error



Within group Variance - Dispertion of scores within each group, cause by error



F- Between group Variance / Within Group Variance

- Measure of differences between groups relative to error

- Just like t, F is influenced by the differences between means as well as the spread of scores in
each group



F=- MS between / MS within



MS (mean squares) between = - SS between / df between