Transcript Probability - University of Central Missouri

MORE ANOVAs
• ANOVA can be done with any number of
factors, between and within
• Dividing the variance changes
• The F-tests are interpreted in the same way
Error Terms
• The denominator of the F-test in any
ANOVA is also called the error term.
• The error term always contains only nonsystematic variance.
• One-Way and Two-Way BS ANOVA: error
term is MS Within Groups.
Higher Order ANOVA
• Factorials may have more than two i.v.’s
• ANOVA on these factorials is called higher
order:
– three way ANOVA for three i.v.’s
– four way ANOVA for four i.v.’s
1
A
2
1
B
1
2
1
A
C
2
1
B
2
2
Effects Tested in Three-Way
ANOVA:
•
•
•
•
•
•
•
A
B
C
AxB
AxC
BxC
AxBxC
three-way interaction: two-way interaction
changes depending on the level of a third i.v.
Example: Therapy, Drug, and Setting are
manipulated in a 2x2x2 factorial. For inpatients, the
effect of the drug is greater for people getting
cognitive than behavior therapy. For outpatients, the
effect of the drug is greater for people getting
behavior therapy.
Drug
Placebo
Drug
Prozac
Placebo
Prozac
20
40
20
60
20
60
20
40
Inpatient
Outpatient
Setting
“Never Eat Anything Bigger
Than Your Head”
• Results of higher-order ANOVAs become
difficult to interpret
• Don’t do the analysis if you won’t know
how to interpret it
• You must always interpret the most
complex effect that is significant