Week 4 Flashcards
What is the Bonferroni Correction?
An adjustment made to p values when several t-tests are being performed
Divide the critical p value (.05) by the number of comparisons being made.
Reduces the chance of making a type I error
Why is an ANOVA used?
To avoid having to run multiple t-tests
Tests the null hypothesis that all groups are the same. Referred to as the omnibus effect
What does an ANOVA do?
Test all your variables against each other and tell you whether it is likely that any of your comparisons are significant
If they’re significant it is likely that some or all of your comparisons are significant so you run post-hoc t-tests
If the ANOVA is not significant then your comparisons won’t be significant so you don’t run post-hoc t-tests.
What is the F value (for between subjects)?
Between Groups Variance / Within Groups Variance
ALSO
Treatment effect + Individual Differences + Error Variance / Individual Differences + Error Variance
If F > 1 there is some effect.
F (between df, within df) = [F value], p = [p value]
What are the assumptions of the independent ANOVA?
1) Continuous DV
2) Normal Distribution
3) No Outliers (extreme scores)
4) Equal Variance - Levene’s test (good if NOT significant)
What is the F value (for within subjects)?
Between Conditions Variance / Within Participants Variance
ALSO
Treatment Effect + Error Variance / Error Variance
What are the assumptions of repeated measures ANOVA?
1) Continuous DV
2) Normal Distribution
3) No Outliers (extreme scores)
4) Equal Sphericity - Mauchley’s test
What does the Mauchley’s test of sphericity tell us?
Whether there is a significant difference between the variances of the differences.
Good if NOT significant.
If it is significant –> read Greenhouse-Geisser to correct this
Is the ANOVA robust to violations?
Yes but if there’s a small number of PPs, skewed data and uneven number of scores it is advised to use nonparametric tests.
What is between groups variance?
The degree of variation between the means of the different conditions.
What is within groups variance?
The variation within the columns, the assumptions of an ANOVA is that the variation in each group is similar
What is within participants variance?
Calculated by finding the average for each PP across each condition and calculating the difference between the PP’s mean and their score in each condition, don’t need to take into account individual differences.
