Single Factor Anova

Question 1

What does ANOVA mean?

Answer 1

Analysis of variance

Question 2

Tell me about factors, levels, experiments and conditions

Answer 2

You have factors: factors have levels
You have experiments: and experiments have conditions

Question 3

What is the difference between single factor anova and two factor anova

Answer 3

What happens to one variable changes depending on what the other variable does. Two factor analysis allows you to assess the potential for multiple things to interact with each other in terms of their influence on something else. Single factor analysis does not do this.

Question 4

What are 9 steps on how to do an ANOVA? (you will not be asked to calculate in an exam)

Answer 4

1) First calculate the grand mean which is to take all data points (add up all data in both conditions, divide by number of data entries and you have an overall grand mean)
2) The calculate the standard deviation
3) Then for each data entry do (data point – grand mean) squared, then add the next one and the next one till you get an overall number.
4) Then you calculate the between-groups variance -> look at the lecture
5) Look at lecture for the rest – then using the between groups variability, the total variability you work our the within groups variability (this is the noisy variability that cannot be due to the manipulation)
6) Then take the sum of squares between groups, the total variability then you convert that into an average.
7) When you report you neeed 2 dfs. One is mean between groups, one with mean within groups.
8) You divide one by the other then you get the f value.
9) Is this F value big or small? When you present the first number is the between groups of freedom, the second is within groups degrees of freedom

Question 5

What are assumptions of single factor between participants ANOVA

Answer 5

• Random and independent samples
• normally distributed “something or other” (See t-tests lecture)
• Equal population variances
• Assumptions are pretty robust to moderate deviations

Question 6

What is Sphericity?

Answer 6

It is a complex thing. It is an assumption for within subject analysis of variance. It is related to the assumption of equal variances for between subject analysis of variance.

If Mauchly’s test of sphericity is significant in SPSS you might have violated the assumption of sphericity. If you have, report Greenhouse-Geiser. Means not have to worry about this assumption.

Question 7

What can you do with an ANOVA that you cannot do with a t test?

Answer 7

You cannot take a T test and apply it to three conditions but with ANOVA you can.

Question 8

What are ‘factors’?

Answer 8

Things we manipulate are called factors.