Experimental Design

• independent groups design

  - different ppts complete in each of the 2 (or more) conditions of experiment

  - ppts randomly allocated to each condition, produces unrelated data

  - ppt variables; if more ppts with a certain characteristic are randomly assigned to one group, can influence DV
• repeated measures design

  - the same ppts complete in each of the 2 (or more) experimental conditions

  - produces related data, each ppt score in one condition can be paired with their own score in other condition

  - order effects; taking part in the 1st condition can influence performance in other conditions
• counterbalancing

  - attempts to control order effects (does not eliminate)

  - uses ABBA format: half ppts complete condition A then B, with the other half completing condition B then A
• adv: IDG

  - ppts less likely to work out the aim than RMD as they only take part in 1 condition; reduces demand characteristics

  - no order effects
• disadv: IDG

  - IGD needs double the ppts compared to RMD for same amount of data

  - ppt variables; between conditions is a problem as they can only take part in one
• adv: RMD

  - RMD needs half the ppts compared for IDG for same amount of data

  - ppt variables; not a problem as ppts take part in both conditions
• disadv: RMD

  - ppts more likely to work out aim of study in IGD as they take part in all conditions; increases demand characteristics

  - order effects; ppt performance can improve/worsen between the conditions due to practice/fatigue
• matched pairs design

  - different ppts complete in each of the 2 (or more) conditions

  - ppts first assessed + ranked on characteristics, then matched to make a pair, then randomly assigned to separate conditions

  - produces related data, reduced ppt variables, no order effects, ppt pairs are similar but not identical