experimental designs

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Research methods
Experimental designs
Independent samples
Completely different participants are used in each condition
No order effects: such as practice and fatigue as participants only do
the experiment once. Practice is when participants will do better in the 2nd
condition as they have already done the experiment in the 1st condition so
will be more familiar with what they need to do. Fatigue is when the
participants may get bored with the experiment in the second condition as
they have already done it in the 1st condition and therefore they will not try
as hard.
Reduces the likelihood of demand characteristics as the participants only
do the experiment once.
Individual differences are more likely as one group may just be natural
better than the other group, therefore this extraneous variable may be
more likely. In order to reduce individual differences, participants are
randomly allocated to the two groups.
Matched pairs
Participants are pre tested on variables that are important in the study. Then
pairs of similar participants (e.g. same gender) are formed and one person from
each pair goes into each condition.
Minimises individual differences by balancing them out due to pretesting
the participants.
No order effects as each group only does the experiment once which also
reduces the likelihood of demand characteristics.
It can be hard to match up people perfectly as there are often lots of
important variables to deal with.
Repeated measures
Participants do the experiment in both conditions.
No individual differences as the same people are used in each condition
Order effects: the participant's performance in each condition may
improve due to practice effects or may get worse due to fatigue effects.
This can be resolved due to counterbalancing (ABBA) when group A does
condition A then B and group 2 does condition B then A. This will balance
out any order effects.
Increased chances of demand characteristics as each participant does
each condition which could invalidate results.


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