Research Methods - psychlotron.org.uk
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Transcript Research Methods - psychlotron.org.uk
Research Methods
Experiments
IV & DV
Hypotheses (directional & non-directional)
Controls
Operationalisation
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Experimental Design
In an experiment we manipulate an IV
There are usually two values of the IV e.g.
Noise or no noise
Rhymes or synonyms
These determine the conditions of the
experiment
The conditions can be arranged in several
different ways
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Experimental Design
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Independent measures
Repeated measures
Matched participants
Independent Measures
Recruit a group of
participants
Divide them
into two
This group does the
experimental task with the
IV set for condition 2
Measure the DV for
each group
Compare the results for the two groups
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This group does the
experimental task with the
IV set for condition 1
Repeated Measures
Recruit a group of
participants
The group does the
experimental task with the
IV set for condition 1
Condition 2
The group repeats the
experimental task with the
IV set for condition 2
Compare the results for the two conditions
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Condition 1
Matched Participants
Recruit a group of
participants
Recruit another
group that
matches them
one for one
Treat the experiment
as independent
measures
Condition 1
Condition 2
Compare the results for the matched pairs
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Find out what
sorts of people
you have in the
group
Participant Variables
Variation between PPs can affect DV
Could mask an effect (false negative)
Could imply an effect where none exists (false
positive)
Control by random assignment to groups
Use repeated measures or matched PPs
instead
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This is a problem with independent
measures
Fatigue, Boredom & Practice
Carrying out a task repeatedly leads to
changes in performance
Deterioration as PPs become tired or bored
Improvement due to practice
Leave a long gap between conditions
Counterbalanced design
Use independent measures or matched
participants
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This is a problem with repeated measures
Counterbalancing
Important control when using repeated
measures
Reduces ‘carry over’ effects
Half PPs do condition A then B
Other half do condition B then A
Fully counterbalanced: ABBA
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Attrition
When PPs drop out of a study (attrition)
data are lost
Fewer data = less powerful study
This can be a problem with matched PPs (and
repeated measures if there is a gap between
conditions)
Loss of a PP in these designs means
losing their data from both conditions
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