Within Subjects Methods

Question 1

Within subjects design

Answer 1

Repeated measures
- participants provide data for each condition of the IV
- not vulnerable to individual differences threats
- but vulnerbale to time and order related threats
- the same participants in each treatment conditoin

Question 2

Advantages to within subjects design

Answer 2

Removes or reduces threats from individual differences (no threat from assignment / selection bias because its the same participants)
- controls individual differences, avoids increased variance (therefore fewer participants are needed as there are greater statistical power) –> useful if special population

Question 3

Disadvantages of within subjects design

Answer 3

vulnerable to
- environmental threats (time of day, treatment / testing location, weather, noise)
- time related factors (history effects, maturation, regression to the mean, instrumentation)
- order effects (carryover effects, progressive error - practice / fatigue)

Question 4

What do we do about order effects

Answer 4

• choose a between-subjects design
• control time
• counterbalance (vary the order of treatments to balance order effects)
  –> if you have multiple treatment conditions, then you need lots of sequences - and if you have the same amount of participants in each experiment, you’re going to have an insane amount

Question 5

What analyses would you use for 2 within subjects conditions?

Answer 5

Paired samples t-test (Wilcoxon for non-parametric)

Question 6

What analyses would you use for repeated measures within subjects conditions (more than 2)

Answer 6

Repeated measures (ANOVA)
Friedman’s ANOVA for non-parametric