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Experimental Design
Recap
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What are IVs and DVs?
Conditions
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In an experiment you can have two conditions
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The experimental condition is where you
manipulate a variable to see the effect
The control condition is where nothing is
manipulated so that we have a base line to compare
our results with.
Conditions
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Identify the conditions:
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An experimenter wants to see if drug X improves
sport performance. One group are given the drug,
another are given a placebo. Both groups are
tested for athletic ability.
Note that not all experiments will have a
control condition (when testing for a
difference between men and women for
example)
Task
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On the handout
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Identify the IV and the DV
Identify the two or more conditions in the
experiment, highlighting which condition is the
control (if there is one)
What do we mean?
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Experimental design refers to how we use our
participants in our experiment
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There are three main ways that participants
can be used.
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Independent measures
Repeated measures
Matched pairs
Repeated measures
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In repeated measures, each participants takes part in
every condition
E.g. to test the effect of caffeine on mood,
participants have their mood assessed, drink a cup of
coffee, then have their mood assessed again.
Control condition:
no caffeine
Experimental condition:
caffeine
=
Repeated Measures
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Strengths
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No participant variables
Fewer participants are needed
Weaknesses
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Risk of demand characteristics
Risk of order effects; boredom, fatigue and
practice effects
Independent Measures
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In an independent measures design, each participant
is only used in one condition
E.g. to test the effect of caffeine on mood, one group
of participants are given coffee, another group are
not. Both groups have their mood assessed before
and after
Control condition:
no caffeine
Experimental condition:
caffeine
≠
Independent measures
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Strengths
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lower risk of demand characteristics
No order effects such as boredom, fatigue, or
practice effects
Weaknesses
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Higher risk of participant variables
More participants are needed
Matched pairs
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Matched pairs is similar to repeated measures, but the
participants in the groups are matched with each other,
so that the two groups are as similar as possible.
E.g. before a study, the experimenter selects two
groups of participants, and matches them on age,
gender and intelligence. One group of participants are
given coffee, another group are not.
Control condition:
no caffeine
Experimental condition:
caffeine
≠
Matched pairs
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Strengths
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Participant variables are reduced
No order effects
Less risk of demand characteristics
Weaknesses
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Participants can never be completely matched
Time consuming and expensive
More participants required
Experimental designs activity
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I am testing the effect of music on
concentration. In my experimental condition I
will play loud music and get the participants
to answer general knowledge questions. In my
control condition I will give a general
knowledge test without music
Experimental designs activity
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Stand up! You are my participants.
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Organise yourself into
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Independent measures
Repeated measures
Matched pairs
Task
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Identify the experimental design used in the
examples