Experimental Designs

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Experimental designs:
as well as knowing how the experiment is being conducted, a researcher needs to decide whcih experimental design is being used
this is the decision about how to allocate participants to different conditions
there are 3 experimental designs: independent measures, repeated measures and matched pairs design
Independent measures design
an independent measures design involves using different people in each condition
Evaluation of independent measures design
S - no order effects
S - reduced demand characteristics
W - individual differences
Repeated measures design
a repeated measures design involves using the same people in each condition. Each participant takes part in both/all conditions
Evaluation of repeated measures design
S - no individual differences
W - order effects
W - increased demand characteristics
Order effects
some investigations will use the same participants in each condition - a repeated measures design. A problem with this is that the particpants may endure the 'fatigue effect' or the 'practice effect'. These are collectively known as 'order effects' as they are caused by the order in which participants complete the conditions
Counterbalancing
to control for order effects you can do something called counterbalancing. This is sometimes known as the 'ABBA method'
half the participants take part in condition A and then complete condition B
half the participants take part in condition B and then complete condition A
this way, it means that if there are any practice effects or fatigue effects then the ordering of the groups cancels this out
Matched pairs design
matched pairs involves using different participants in each condition, but participants are 'matched' or paired with another who is similar in a number of variables
Evaluation of matched pairs design
S - reduced individual differences
S - reduced demand characteristics and no order effects
W - there are still some participant variables