experimental designs

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Research methods revision
Experimental designs
Independent samples: completely different participants are used in each
no order effects such as practice and fatigue as participants only do the
experiment once. Practice is when participants do better in the 2nd
condition as they have already done it in the 1st condition so they
understand what to do better. Fatigue is when participants get bored with
the experiment in the 2nd condition as they have already done it in the first
so they try less hard.
Reduces demand characteristics as participants only do the experiment
Individual differences are more likely as one group may be naturally
better than the other group. Therefore this extraneous variable could be
more likely. In order to reduce this participants are randomly allocated to
2 groups.
Matched pairs: participants are pretested on variables important to that study.
Then pairs of similar participants are formed and 1 person from each pair is put
into each condition.
Minimises individual differences by balancing them out be pretesting
No order effects as each participant only does the experiment once
reducing the likelihood of demand characteristics
Hard to match perfectly as there can be lots of variables to consider
Repeated measures: participants do the experiment in both conditions
No individual differences as same people do each condition
Order effects as participants' performance in each condition may
improve due to practice effects or may get worse due to fatigue effects.
This can be solved through counter balancing (ABBA) when group 1 does
condition A then B and group 2 does condition B then A. This balances out
any order effects.
Increased demand characteristics as each participant does both
conditions leading to invalid results.


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