Experimental designs Flashcards
Why experimental designs?
When carrying out experiment, psychologists must decide on how they are going to use/distribute their participants effectively.
3 types:
Independent groups design
Repeated groups design
Matched pairs design
Overview: the sample of participants must first be selected before allocation to experimental designs can occur.
What is independent groups design?
Different participants are used in each condition of the experiment
If there are 2 levels of the IV this means that some participants will take part in the experimental condition, while the other group is the control group
The allocation of participants to groups should be by random allocation, which ensures that each participant has an equal chance of being assigned to one group or the other.
Strengths of independent groups design
Order effects - are avoided - participant only take part in one condition so they cannot get better/worse between conditions, they cannot get tired and bored
Demand characteristics - are avoided - participants only take part in one condition so less likely to guess the aim of the study and alter their behaviour accordingly
Limitations of independent groups design
More participants are required - to produce the same amount of data as repeated measures design (can be more time consuming to recruit more)
Participant variables - a difference between the groups might be because of the characteristics of the group rather then manipulation of the DV
What is repeated measures design?
The same participants take part in both conditions of the experiment
This means that each condition of the experiment includes the same group of participants
Strengths of repeated measures design?
Fewer participants are required - all participants are taking part in all conditions (therefore less time consuming to recruit participants)
Participant variables are controlled = there are no individual differences between the groups as the same people are taking part in both
Limitations of repeated measures design?
Order effects = the order of the conditions may have an effect on behaviour, some ppl may have improved between conditions. some may have declined
Demand characteristics = participants are more likely to work out the aim of the study as they are taking part in two conditions and therefore may alter their behaviour
What is counterbalancing?
An attempt to control for the effects in a repeated measures design: half of the participants experience the conditions in one order (A then B) and the other half is an opposite order (B then A)
Order effects are happening both ways
What is matched pairs design?
Pairs of participants are matched in terms of key variables such as age
One member of each pair is then placed on the two different conditions
Strengths of matched pairs design
Participant variables are reduced - the researcher has tried to match the participants as much as possible on important aspects
Order effects are avoided - ppl only actually take part in one condition so they cannot get bored, tired or better in between.
Demand characteristics are reduced - ppl less likely to guess the aim as only take part in one condition.
Limitations of matched pairs design
Time consuming and expensive to match participants
Individual differences still occur - the matching of participants can never be exact so participant variables still affect the experiment
What are the 4 types of experiment ?
Laboratory, field, natural and quasi
What are laboratory experiments?
Takes place in controlled environment
Researcher manipulates the IV and records effect on DV
Maintaining strict control of extraneous variables
What are field experiments?
An experiment that takes place in a natural setting within which the researcher manipulates the IV and records effect on the DV
Researcher records effect on DV
