Researcg Methods - experimental designs

Repeated measures definition

The same participants are used in each condition. This means the participants would be tested in one condition and then at some point be tested again in the other condition

RM advantages

Amount of participants - as the participants take part in both conditions, less participants are needed compared to IG or MP

No unbalanced groups - participants variables are controlled as the same participants are used in each condition. This makes the research higher in validity

RM disadvantages

Order effects - the order of the conditions may affect the participants behaviour. Participants may do better on the second test because of a practice effect or participants may do worse on the second test because of being bored with doing the same tests again ( bored or fatigue effect )

Demand characteristics - there is a greater chance that participants wil guess the aims of the research because they are taking part in both conditions. If they do know the aims and change their behaviour this would affect the internal validity of the research.

Independent groups definition

Different participants are used in each condition. Each participants will only experience one condition of the study .

IG advantages

Order effects - there are no order effects ( practice or fatigue / boredom effects ) influencing the results because a different group of participants are taking part in each condition.

Demand characteristics - as the participants only take part in one condition it is highly unlikely that participants will guess the aims of the research and change their behaviour.

IG disadvantages

Amount of participants - more participants are needed compared to a RM design as you need two different groups of participants ( one group for each condition )

Unbalanced groups - participants who occupy the different groups are not the same in terms of participant variables. Individual differences between participants may act as a confounding variable, reducing the validity of the findings.

Matched Pairs definition

Different participants are used in each condition but each participant in group A , is paired with a participant in group B. This is done by pairing them based on key characteristics that might be relevant to the research e.g IQ, memory, gender, or age and then placing one member from each pair in each condition

MP advantages

Attempts to eliminate unbalanced groups - as the participants have been paired on variables relevant to the research BEFORE being randomly assigned to one condition this should prevent participant variables from affecting the research.

Demand characteristics - participants only take part in one condition so they are far less likely to guess the aim of the research and change their behaviour. This helps to preserve the internal validity of the research.

MP disadvantages

Amount of participants - as participants only take part in one condition you would need to recruit more participants than you would if using a RM design.

Time consuming and difficult to achieve - although there is some attempt to reduce participant variables in this design, participants can never be matched exactly. Matching may be time consuming and expensive, particularly if a pre test is required so this is less economical than other designs.