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Experimental research is a comparison-between-
The experimenters are seeking to discover or
corroborate cause and effect relationships by
changing something to see if the change causes a
difference to another thing.
They alter the independent variable (IV) to see if
it causes a difference to a dependent variable
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A Classic, experimental method involves
assigning subjects at random to either an
‘experimental’ group or a ‘control’ group.
The ‘control’ group is compared with the
‘experimental’ group to assess the effects of
the experiment on the experimental group.
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Switching on the light
The independent variable(IV) can be
likened to a light switch and the dependent
variable (DV) can be likened to a light bulb.
An experiment compares the results of
exposure of one (independent) variable
upon another (the dependent variable).
Switch on (the IV ‘switch’) and the (DV)
bulb (metaphorically) illuminates the room.
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Advantages of experimental
The experiment is probably the best scientific
method for attempting to prove or corroborate
It allows us to locate the variables which control
or cause a problem to occur.
For some researchers such as those in the physical
sciences the experiment has good internal validity
because of the degree to which all ‘extraneous’
variables are controlled.
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The experimental process
Consider-as a group-how we could set up an
experiment to discover the impact of noise
upon the recall of radio news.
How could we test the hypothesis that noise
affects recall of radio news?
What would we need?What is the IV
‘switch’? What is the DV ‘light bulb’ being
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The noise hypothesis –1
1. Select two groups. (caveats/qualifiers?)
2. Expose them to the same news broadcast.
3. One is under ‘noisy condition’ and other is
under ‘silent condition’.(definitions?)
4. After exposure to the news each group is
tested separately,using same recall
test.(test admin. Issues= ?)
5. IV=noise and DV=recall of news content.
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Aims of experimental research
Establish cause and effect relationships.
Then, like a switch we can turn the phenomena
‘on’ and ‘off’.
This is useful as the ability to switch things on or
off means, a) we can be reasonably confident
we’ve found variables that cause or impact on the
problem significantly, and b) we can use that
knowledge to control or adjust such phenomena.
Such knowledge has advanced natural science and
medicine as mentioned.
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Issues in any experimental
Internal validity--This is summed up in the following
question -Does the experiment test what we say it tests?
How sure can we be that the changes in the DV we
measured were caused by the changes in the IV?
Are all extraneous variables or ‘confounding’ variables (ie
one which changes as IV changes) controlled?
For example, how sure can we be about the ‘noise’ and
recall of news experiment’s internal validity?
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Possible alternative explanations
or extraneous variables?
Boredom-don’t listen to news normally and not
interested in the experiment.
Nothing else to do-cognitive dissonance ie make it
seem better use of time/less of a waste of valuable
Trying to curry favour by participating in
Non-aural learner eg visual or tactile or sociable
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External validity means how strong are the
generalizations we can make from this
research (if any)?
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Threats to validity of
Campbell in Bynner & Stribley (1978) identified 9
threats to internal validity and 6 to external
Internal validity threats
1. History : mediating event or factor between pre-
and post-test= alternative possible explanation
of effects.e.g. Easterby and Ashton’s study of
University Management Development
Programme’s Impact on students’ careers.
(Managers’ Colleagues used absences to their own advantage).
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More threats to internal
validity of experiments
2. Maturation:changes in subjects or society such
as growth,fatigue, social trends.
3. Instability:instability of measures, sampling
fluctuations or of repeated or ‘equivalent’
4. Testing:The effect of taking a first test upon a
second or subsequent test or the effects of one
social indicator upon future readings of that
indicator e.g. ‘priming’ subjects ,stock prices.
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Even more threats
5. Instrumentation:changes in calibration of
equipment, or observers, or scores used.
6. Regression artifacts: so-called ‘pseudo-shifts’
which occur when people or treatment units
have been selected upon the basis of their
extreme scores.ie. Regression to the ‘norm’ or
middle scores in following groups or years eg
selection of years of droughts or floods or high
fatality years-following years may show
improvement even if ‘untreated’.
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Yet other threats
7. Selection: bias resulting from differential
recruitment of comparison groups-leads
to different mean scores for measures of
8. Experimental mortality: Loss of people
from comparison groups ( they die, they
move, they get new jobs etc).
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Finally--Interactive threat to
9. Selection-maturation interaction:
selection biases resulting in different rates
of maturation or autonomous change. Eg
on e group matures quicker than another
causing selection bias.
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Threats to external validity
and interpretation of results
1. Interaction effects of testing- ‘priming’.
2. Interaction of selection and ‘treatment’-
unduly ‘responsive’ outcomes.
3. Reactive effects- ‘articifiality’ &
4. Multiple treatment interference-
cumulative effects untypical of separate
treatment eg First Gulf war syndrome
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5. Irrelevant responsiveness measures-
complex measures,some irrelevant ones
may appear to produce effects.
6. Irrelevant replicability of treatments-
complex treatments & replications may
‘forget’/omit some components actually
responsible for the effects.
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Social science experiments
Asch(1955)-Opinion & social pressure
Ekman et al (1987)-Universals & cultural
differences in judgments of facial expressions of
Milgram (1964)-Obedience to authority
Gordon(1992)Treatment of depressed women by
Zimbardo(1974)-psychology of imprisonment