Experimental Designs


Repeated Measures Design

: each ppt takes part in every condition


+ No individual differences between ppts in different conditions


- Risk of order effects, i.e. practice effect - performance might be better in the second condition because the ppts know what to do

*The main way order effects are dealt with is using counterbalancing - Alternating the order in which ppts perform in different conditions of an experiment

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Independent Groups Design

: ppts are allocated to two (or more) groups, and then take part in different conditions of the experiment


No order effects (because ppts only take part in one condition, depending what group they're in) 


More time consuming (as more ppts are needed)

More expensive (if ppts get paid)

Differences between ppts in the groups may affect results - e.g. ppts in Group A may have better memory than ppts in Group B) - these are known as extraneous variables

*These differences can be avoided by randomly allocating ppts to groups

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Matched Pairs Design

: pairs of ppts are matched in terms of characteristics such as age and IQ etc.


Lower risk of demand characteristics 

No order effects (same procedure as Independent Groups)


- Matching pairs of ppts may be time-consuming and difficult

- Large number of potential ppts needed to achieve matching 

Not possible to control all ppt variables

* In order to control ppt variables, conduct a pilot study to consider key variables that might be important when matching 

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