| The experimental method is a controlled procedure that sees the manipulation of an independent variable (IV) in order to observe or measure its effect on a dependent variable e.g. levels of alcohol and measured effect on reaction time. |
 The experimental method of research is a controlled procedure
that sees the manipulation of an independent variable (IV) to observe and measure any effect
this has on a dependent variable (DV). The essential features of the experimental method are
then the control, observation and measurement of variables. Illustrating the hallmarks of a
science, the use of the experimental method in psychological research makes us more confident
about the validity of any cause-effect relationship established between an independent and
dependent variable. The experimental method also makes us more confident about the
generalisation of its results to a wider population. The experimental method's emphasis on
strict procedures helps others replicate the experiment to confirm, or otherwise, the original
research findings. This is how scientific knowledge grows. The experimental method sets out to
test a null hypothesis, which if rejected allows the researcher to accept the experimental, or
research, hypothesis. Hypotheses will, more often than not, be tested at a level of
significance. A level of significance is the wager, probability, or p value a researcher places
on themselves that their results happened by chance. Students of psychology generally set
themselves a level of significance of 1:20, which means they are happy to accept that in the
rejection of their null hypothesis, there is still a 5% chance that any cause-effect
relationship established by the acceptance of the experimental hypothesis is because of chance
or random factors. These chance or random factors, which can be an alternative explanation for
results in psychological research, are called
extraneous variables and are of two kinds. Random
variables just happen, making them impossible to control, and
confounding variables, which can be anticipated and controlled. Examples of confounding variables would be any situational variable
found in the experimental setting, experimenter variables,
such as experimenter and expectancy effect, and
participant variables, which are those participant peculiarities that can influence results. These
would include participant expectancy and demand characteristics. To control for extraneous variables
the experimental method uses a design procedure, which are of two kinds. A related, or
within-subjects design like repeated measures
or matched pairs, and alternatively, a
between-subjects design and unrelated independent group /
sample / measures design. Each category, and each type of design has particular features. For example,
the repeated measures design, where participants experience all conditions/manipulations of the independent
variable, can as we know attract order effect.
Counterbalancing can of course control
order effect. What design is adopted is often decided in anticipation of confounding variables that c
an arise in the different experimental situations, which are the
laboratory, field and
quasi-experiment. They differ in their location,
and thus the degree of control a researcher has over confounding variables. The laboratory experiment often
attracts criticism on the grounds of ecological validity. They are sometimes 'No' real '! The
further away from the laboratory a researcher goes however, the more likely that the more
ecologically valid quasi- or field experiment attracts random and confounding variables. As a
research method, the experimental method is assuredly the most rigorous of methodologies in
psychology. |
| Type of Experiment | ||
| Laboratory Experiment |
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| Field experiment |
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| Quasi experiment |
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