Experimental Design Flashcards
What is experimental design?
“The different ways in which participants are allocated to the different conditions (IV levels) in an experiment.”
What are the 3 types of experimental design?
Independent group
Repeated measures
Matched Pairs
What is independent group design
In an independent group design, participants only take part in one condition.
They are either in the control condition or in the experimental condition.
What is a repeated measures design?
In a repeated measures design, participants take part in both conditions.
They are in the control condition and in the experimental condition.
What is matched pairs design?
In a matched pairs design, participants only take part in one condition. However, before being allocated to either the control condition or the experimental condition, they are ‘matched’ with another participant on key variables relevant to the experiment. For example, in our caffeine and talking experiment, we might pair two participants who are of similar levels of extrovert-ness. One of the pair is then allocated to the control condition and the other to the experimental condition.
Independent group +’s?
There will be no order effects – ppts only complete one condition so they will not become bored or get better (practice effect). Increases the internal validity
Less chance of demand characteristics. Ppts take part in only one condition, they are less likely to work out the purpose of the study and change their behaviour to help or hinder. This increases the internal validity of the study
Independent group -‘s?
Requires more participants than as the researcher will need to get two separate groups of ppts to end up with the same amount of data
Impossible to control all participant variables because only the key ones can be matched for – there could be others which could effect the research. This lowers the internal validity
Repeated measures +’s?
Requires fewer participants as ppts take part in all conditions. Meaning a potentially larger sample can be used. Increasing external (population) validity
Participant variables are removed e.g. IQ/Age as ppts take part in all conditions. Increasing the internal validity.
Repeated measures -‘s?
Results may be affected by order effects – participants may become bored by the second condition and so do less well or better (practice effect). Lowers the internal validity.
Increased chance of demand characteristics as when ppts do the second condition they may work out the purpose of the study and change their behaviour to help or hinder. Lowers the internal validity.
Matched pairs +’s?
Controls for individual differences/ participant variables i.e. ppts are matched on one or more key characteristics such as age, IQ, gender that may affect the results. Increasing the internal validity.
There will be no order effects – ppts only complete one condition so they will not become bored or get better (practice effect). Increases the internal validity.
Matched pairs -‘s?
The most time consuming experimental design as the researcher needs to identify all important participant variables and spend time matching participants
Individual differences/participant variables i.e. the different characteristics of the participants such as age, gender may affect the results. Lowers the internal validity.
How to minimize individual differences/participant variables?
This can be minimised by randomly allocating participants to the two conditions. The laws of probability would suggest that by randomly allocating participants to one of the two conditions (e.g. placing pieces of paper saying ‘control’ or ‘experimental’ in a hat and having the participants pull one out), then participant characteristics will be evenly distributed across the conditions.
How to minimize order of effects?
In counterbalancing, half of the participants firstly take part in condition A (the experimental condition) and then they take part in condition B (the control condition).
The other half do it the other way round – condition B (control) followed by condition A (experimental).
This ‘balances out’ any order effects.
