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PSYC 230 Final Exam
•
OneWay ANOVA
: means one independent variable
o
Independent Variable: (should have
at least three levels)
each level is a group of subjects
o
Dependent Variable: (only one dependent variable)
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What is “within” group variance?
o
This is what we’ve been doing whenever we have been figuring standard deviations of
curves
o
Error Variance
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How is ANOVA different from ttests
:
1.
ANOVAs can test more than two means
2. We are comparing sample means indirectly by comparing sample variances
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Means and Significance:
By comparing the within group and between group variance we are able to answer
questions about
whether the differences between the means of groups are
significant
•
Sum of Squares between groups
sum of the squared deviations of group means about the overall mean
•
Sum of squares within groups
:
sum of the squared deviations of all scores about their respective group means
1
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Sum of squares total:
sum of the squared deviations of all scores about the overall mean sum of squares:
SS
within
+ SS
between
•
Mean square within groups:
sum
of squares within groups divided by its degrees of freedom
•
Mean square between groups:
sum of squares between groups divided by its degrees of freedom
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Pvalue:
o
Is it less than .05?
o
pvalue is smaller than 0.05 so we do reject the null hypothesis
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When the null hypothesis is true
:
o
the ratio of the betweengroups population variance (estimate) to the within
groups
population variance (estimate) should be about 1.
o
When the research hypothesis is true, this
ratio should be greater than 1
•
The primary difference between oneway and twoway ANOVAS
:
o
Oneway ANOVAs test only one independent variable
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 Spring '08
 Delaney

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