Experimental Designs

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Repeated Measures

The Same participants took part on all conditions of the experiment.

E.g. Levels of processing (all three questions were answered by all participants) 

Strengths

(+) This is the best way to control differences, as each person is compared to themselfs

(+) need fewer participants

(+) intellegence and motivation will be the same

Weaknesses 

(-) The order in which the two conditions are performed could influence the results - these are called ORDER EFFECTS 

(-) People may find it easier to work out the aim of the study 

(-) Both conditions must be similar (Tests must be well matched) 

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Controlling ORDER EFFECTS

To deal with order effects you should COUNTERBALENCE the conditions 

1    2 

AB BA 

For example 

 condition 1                                                         Condition 2 

A= music on                                                       B= Music off 

B= music off                                                       A= Music on

Half of the participants do A then B, and the other half do B then A this prevents tiredness or motivation becoming an exreanous variable

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Independent Groups

People doing both conditions are different, so these alternations can affect the study (adds more extranous variables 

Strengths 

(+) There are no problems with order effects 

(+) Participants are less likely to work out the aim of the study 

(+) Both groups can do the same test 

Weaknesses 

(-) randomly allocating poeple to two conditons should spread extraneous variables across the study

(-) A large sample will reduce the effects of individual differences 

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Matched pairs

Matched pairs involves people allocated into a pair, by similarities of important exraneous variables , and separating them into either conditions 

Twin studies are the best matched pair design 

Strengths 

(+) More control over extraneous variables 

(+) No order effects 

(+) less likely to work out the aim of the study 

(+) same tests can be used 

Weaknesses 

(-) Still some extraneous variables as it is not a perfect match 

(-) matching can be time consuming and difficult 

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