Statistics for Psychology
Brief Homework 5
Analysis of Variance
1. Why are ANOVAs so popular in
psychological research?
The Anovas are so popular in psychological research because
they allow examination of more than two treatment
conditions, and more than one independent variable, allowing
for a more complex look at overdetermined behavior.
They are, essentially, very flexible.
It also controls for family-wise alpha as compared to
performing a number of t-tests.
Finally, with two or more variables, it allows for the
examination of interactions between variables.
2. Explain the logic of separating variance and what the
resulting F statistic represents in the between-groups Anova.
The Anova separates the total variance of all the scores into
different variance components.
Total variation of all scores
Variation within groups
Variation between groups
This allows one to then create a ratio to get an F value that
represents something about just the treatment
F=
between groups variation
within groups variation
=
treatment effect + error
error
3. Explain what an interaction is in a two-way ANOVA.
An interaction exists when the effects of one variable depend
upon the level of the another variable. In a sense, the two
variables combine to create behavior that could not be explained
by either one alone. Found by the cell means.
None
Cog
Beh
means
Female
5
7
9
7.5
Male
6
9
4
7.5
5
6
7
means
New Extended Family
What Testing?
Sample vs. Population
2 Samples
μ&σ
μ only
Between
Within
Single
Sample
z-test
Single
Sample
t-test
Ind
Samples
t-test
Dep
Samples
t-test
3 + Samples
Anova
If parametric assumptions not met, use a
non-parametric equivalent