MEM 09 - Experimental design (MET) Flashcards
What is experimental design?
The different ways in which participants can be organised in relation to the experimental conditions
What is independent group design?
Participants are allocated to different groups where each group represents one experimental condition
What is repeated measures?
All participants take part in all conditions of the experiment
What is matched pairs design?
- Pairs of participants are first matched on some variable(s) that may affect the dependent variable
- The one member of the pair is assigned to Condition A and the other to Condition B
What is random allocation?
An attempt to control for participant variables in an independent groups design which ensures that each participant has the same chance of being in one condition as any other
What is counterbalancing?
- An attempt to control for the effects of order in a repeated measures design
- Half the participants experience the conditions in one order, and the other half in the opposite order
What are the strengths of independent group design?
- Lower risk of demand characteristics as participants are less likely to guess the aims if they are only carrying out one of the conditions
- No order effects
What are the weaknesses of independent group design?
- One big issue is that there are individual differences between the participants who occupy the different groups in terms of participant variables (may not always perfectly balance characteristics). This means if a researcher finds a mean difference between the groups on the DV this may be more due to participant variables rather than the IV.
- These differences may act as a confounding variable reducing the internal validity of the findings
- Independent group designs are less economical than repeated measures as each participant contributes a single result only.
- Meaning twice as many participants would be needed to produce equivalent data to that collected in a repeated measure. This increases the time/money spent on recruiting participants
How can the weaknesses of independent group design be dealt with?
Random allocation of participants to conditions
What are the strengths of repeated measures?
- Participant variables/individual differences are controlled therefore higher internal validity
- Fewer participants are needed (therefore less time spent recruiting participants)
What are the weaknesses of repeated measures?
- The biggest issue for repeated measures is that each participant must do at least two tasks, and the order of these tasks may be significant (i.e. there are order effects)
- Order effects also arise because repeating two tasks could create boredom or fatigue that might cause deterioration in performance on the second task, so it matters what order the tasks are in. Alternatively, participants’ performance may improve through the effects of practice especially on skill-based tasks
- Order acts as a confounding variable
- High risk of demand characteristics => participants may work out the aim of the study when they experience all conditions of the experiment
How can the weaknesses of repeated measures be dealt with?
Order effects can be dealt by using counterbalancing
How can the weaknesses of matched pairs be dealt with?
Random allocation of matched pairs to conditions
What are the strengths of matched pairs?
Participants only take part in a single condition, so order effects and demand characteristics are less of an issue
What are the weaknesses of matched pairs?
- It is difficult to match participants perfectly, there will still be important differences between them that may affect the DV
- Matching may be time-consuming and expensive, particularly if a pre-test is required, so this less economical than other designs
