Week 1: secondary variables, invalidity, reporting

Question 1

What is the aim of experimental designs?

Answer 1

To establish a causal link between a variable (manipulated by the experimenter) and some measure fo the participants response

Question 2

What are some ways of controlling extraneous variables?

Answer 2

Elimination: removing it - sometimes not possible so…
Constancy: you can make it constant
Making it into an IV: deliberately collecting its data
Randomisation: smearing effects across groups
Statistical adjustment: more complex

Question 3

What are some sources of invalidity in experimental design? (change in DV may not be due to IV)

Answer 3

Proactive history: subject variables that you can minimise though elimination etc
Retroactive history: happens during experiment
Repeated testing: learning or sensitisation from previous tests
Statistical regression: extreme scores moving closer to the mean if retesting. control groups to fix
Maturation: natural change
Loss of subjects: people drop out
Interaction effects: previous treatment effects subsequent
Error in DV measurement
Experimenter bias
Errors in statistical inference

Question 4

What are ANOVA and t tests used for?

Answer 4

To compare the differences in means

Question 5

What is the null hypothesis?

Answer 5

Equal means
Difference = 0

M1=M2 (=M3 in ANOVA)

Question 6

How do you report t-tests?

Answer 6

Means & SDs
Sample sizes
t(df)=t, p=p

Question 7

When there are only two groups, what is the relationship between t and f stats?

Answer 7

F = t(squared)

Question 8

When you have more than 2 means and conduct an ANOVA, what do you do if it is significant?

Answer 8

Need to do post hoc tests to see where the differences are

Question 9

How do you report an ANOVA

Answer 9

Means, SDs, sample sizes
F(df, df)= F, p=p

Explain more about the DV, groups, experiment etc