1st ANOVA lecture: 1-way ANOVA and post-hoc testing

Question 1

When to use ANOVA

Answer 1

When you want to compare the mean of a continuous DV between more than 2 groups on a single categorical IV

When you want to compare the mean of a continuous DV between 2 or more groups on 2 or more categorical IVs.

Question 2

F-ratio

Answer 2

Statistic that tells you how much variability in results is accounted for by ANOVA and how much by RV (random variability). Tells you if the main effect is statistically significant.

F-ratio = Mean squares (model)/mean squares (residual error)

If F-ratio is significant then further exploration of that IV is appropriate.

Question 3

Levene’s test

Answer 3

For homogeneity of variance. Used in Independent groups ANOVAs.

Question 4

Mauchly’s test of sphericity

Answer 4

Used in repeated measures ANOVAs to check the variance of each IV level is similar (and covariance between pairs of levels is also similar). Equivalent of homogeneity of variance for independent groups.

Question 5

DV must be on an:

a) categorical scale
b) interval scale
c) continuous scale
d) b and c

Answer 5

d) DV must be on a continuous and interval scale meaning there is an equal distance between variables.

Question 6

What is meant by independent sampling?

Answer 6

Each participant can’t have had prior knowledge or have been influenced by another participant in the group (each participant’s performance is independent from each others). This is one of the assumptions of an ANOVA.

Question 7

What are the 3 assumptions common to both independent groups ANOVAs and repeated measures ANOVAs?

Answer 7

• Independent sampling
• DV on an interval scale
• Normally distributed data within levels

Question 8

What is a Kolmogorov-Smirnov test?

Answer 8

A nonparemetric test for the equality of continuous, one-dimensional distributions that can be used to compare a sample with a reference probability distribution (ie: tests whether distribution normal). Don’t want this to be significant.

Question 9

Kurtosis

Answer 9

The sharpness of the peak of a frequency-distribution curve.

Question 10

Skewness

Answer 10

A measure of the assymetry of a probability distribution about the mean.

Question 11

If the right tail is longer the skew is…

Answer 11

Positive. The distribution is concentrated on the left side.

Question 12

What is the difference between the way you would input data for independent groups on SPSS compared with repeated measures?

Answer 12

In independent groups the levels of the IV are nested within the same column. In repeated measures the levels are separated into different columns.

Question 13

If p>.05 on Levenne’s test what does this mean?

Answer 13

Equal variances can be assumed.

Question 14

What does SSR refer to?

Answer 14

The variability not explained by the IV.

Question 15

What are the benefits and limitations of p being less than 0.05?

Answer 15

Benefits: tells you that some variability in the sample is systematically explained by the IV and is likely to be replicated in the population.

Limitations: does not tell you size of this effect.

Question 16

Whether the result is clinically significant depends on:

a) The p value or
b) The effect size

Answer 16

b) the effect size

Question 17

Which is a better estimate of effect size?

a) Eta squared or
b) Omega squared

Answer 17

Omega squared. It adjusts for random error so provides a more accurate estimate of the likely effect size in the population.

Question 18

What is partial Eta Squared?

Answer 18

Proportion of variance uniquely explained by the variable. Used for calculating effect size in repeated measures ANOVA. However, omega squared is still recommended over this even though the calculation is not available on SPSS.

Question 19

What is meant by the family-wise error rate?

Answer 19

An increased number of paired comparisons mean the 1/20 risk each time adds up to increase the risk of a type 1 error being made.

Question 20

What is a type 1 error?

Answer 20

Falsely rejecting the null hypothesis when it is true.

Question 21

What is the Bonferonni correction?

Answer 21

Work out how many pairwise comparisons you are going to do and divide the significance value by these. to reduce the risk of making errors.

Question 22

The best post-hoc test(/s) when all assumptions are met:

Answer 22

REGWQ or Tukey. Tukey useful when making lots of comparisons.

Question 23

When taking a conservative approach and making few comparisons this is the best post-hoc test to use:

Answer 23

Bonferonni

Question 24

When taking a conservative approach and making many comparisons this is the best post-hoc test to use:

Answer 24

Tukey

Question 25

Post hoc tests to use when conditions have unequal sample sizes:

Answer 25

Gabriel’s or Hochberg’s GT2

Question 26

Post hoc test to use when conditions have unequal variances and sample sizes:

Answer 26

Games-Howell

Question 27

Planned contrasts is used when…

Answer 27

we are only interested in making 1 or 2 comparisons that are hypothesis driven. This has the ideal balance between reducing risk of type 1 and 2 error (as corrections have a risk of type 2 error).