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
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
