LECTURE 6: ANOVA

Question 1

ANOVA tests the null hypothesis that

Answer 1

means are the same
meanA=meanB=meanC (etc)

Question 2

What is an omnibus test?

Answer 2

overall test-test of number of different comparisons at once
*will say there is an overall difference! tells that means are diff, but not exactly which means are diff

Question 3

one way independent ANOVA

Answer 3

3 independent groups, 1 DV
ex.
1. placebo
2. viagra
3. high viagra
DV: libido

Question 4

what does F(2, 12) = 5.12 mean?

Answer 4

F =ANOVA statistic
2 = 2 groups
12 = sample n
5.12= calculated F

Question 5

planned contrast is…

Answer 5

a priori test to determine where difference is!
statistical advantage, but can’t change later. ex. compare placebo to group1 and placebo to group3

Question 6

how can you find where group differences lie in ANOVA?

Answer 6

1. planned contrasts (1 group to 2 and 1 to 3)
2. post hoc comparisons (not planned, compares all pairs of means!)

Question 7

post hoc comparisons are…

Answer 7

pairwise comparisons of all
designed to control alpha level (overall error rate)

Question 8

Bonferroni and Tukey control for

Answer 8

type 1 error
*used if only small deviations from normality, sample sizes are equal, HOV met
(B more power than T if less pairs, Tukey more power than B if more pairs)

Question 9

If ANOVA is significant and variances between pairs are not homogeneous, use ____ post-hoc comparison

Answer 9

Games-Howell
accurate with unequal sample sizes (but better with larger samples)

Question 10

If data doesn’t meet assumptions in independent one way ANOVA, use ____

Answer 10

Kruskal-Wallis test

Question 11

If there is more than 1 independent variable, it is called a

Answer 11

FACTORIAL ANOVA

Question 12

If parametric assumptions are met, then independent one-way ANOVA. If significance found, do

Answer 12

post-hoc comparisons: bonferoni or tukey (not HOV: games-howell)

Question 13

If independent one-way ANOVA does not meet assumptions, do

Answer 13

Kruskal-Wallis
post hoc comparison: Mann-Whitney U (nonparametric equivalent to independent t-test)

Question 14

If assessing 1 group over time (3 or more times), must meet __ assumption

Answer 14

SPHERICITY: variances of differences btwn all possible pairs of groups are equal.
then do Repeated measures ANOVA
Bonferroni correction

Question 15

what is sphericity?

Answer 15

variances of differences between all possible pairs of groups are equal

Question 16

what test do you use for sphericity?

Answer 16

Mauchley’s test
*assumption for RM one-way ANOVA

Question 17

If RM one way ANOVA assumptions not met, what is non-parametric equivalient?

Answer 17

Friedman’s Anova
post-hoc comparisons: Wilcoxon Signed Ranks

Question 18

what is the benefit of factorial ANOVAS?

Answer 18

can look at how variables interact
(interactions look for relationships btwn independent variables)
*effeect of IV on another IV

Question 19

The 3 tests for an omnibus factorial ANOVA

Answer 19

1. interaction
2. main effect for 1 IV
3. main effect for 2nd IV

Question 20

If interaction is significant in independent ANOVA, then run

Answer 20

simple effects (forget main effects)
*adjust alpha level!

Question 21

If main effects are significant but interaction is NOT, then run

Answer 21

follow up main effect post-hoc comparisons and ADJUST ALPHA (3 groups = run bonferoni
OR NO FOLLOW UP IF ONLY 2 LEVELS

Question 22

what is a covariate?

Answer 22

extra/confounding variable that can affect outcome variable
(will strengthen analysis and more likely for you to find significance if you account for it: ANCOVA)

Question 23

when do you use MONOVA?

Answer 23

when testing for differences btwn groups when you have several dependent variables
CONTROLS TYPE 1 ERROR (takes into account relationships btwn dependent variables)

Question 24

what is the next step after significant global manova?

Answer 24

discriminant function analysis
(determine with of the DVs are best at separating the independent variables)