The experimental method is
usually taken to be the most scientific of all methods, the 'method of
choice'. The main problem
with all the non-experimental methods is lack of control over the
situation. The experimental
method is a means of trying to overcome this problem.
The experiment is sometimes described as the cornerstone of
psychology: This is partly due to the central role experiments play in
many of the physical sciences and also to psychology's historical view of
itself as a science. A considerable amount of psychological research uses the
An experiment is a study
of cause and effect.
It differs from non-experimental methods in that it involves the
deliberate manipulation of one variable, while trying to keep all other
Experiments in the Laboratory:
experiments (like experiments in other fields) we try to keep all aspects
of the situation constant except one - the one we are looking at. For example, suppose we want to investigate which of two
methods is more successful at teaching children to read. The aspect that we vary is called the independent variable (IV) and we change this in a very precise way.
In this example the teaching method is the independent variable. We
call the factor which we then measure, in our example it would be some
measure of the childrens reading ability, the dependent
variable (DV), because, if our ideas are correct, it depends on the
independent variable. In our
example, the childrens reading ability depends
on the teaching method used.
The variable which is
being manipulated by the researcher is therefore called the independent
variable and the dependent variable is the change in behaviour measured by
All other variables which
might affect the results and therefore give us a false set of results are
called confounding variables
(also referred to as random
variables). Examples of
confounding variables in the example given might include the following
Differences in the instructions given by an experimenter or
in the stimulus materials being used (which could be overcome by
standardising instructions and materials foe all those taking part)
Differences between participants, e.g. in their age (which
could be eliminated as a variable by using a single age group, or
alternatively it could be made more constant by ensuring that the age
structure of each of the groups taking part in the experiment is very
By changing one variable
(the IV) while measuring
another (the DV)
while we control all others, as far as possible, then the
experimental method allows us to draw conclusions with far more certainty
than any non-experimental method. If the IV is the only thing that is changed then it must be
responsible for any change in the dependent variable.
Probably the commonest way
to design an experiment in psychology is to divide the participants into 2
groups, the experimental group
and the control group, and then
introduce a change for the experimental group and not the control group.
Suppose we wish to see if people sit at a library table for a
shorter time if someone comes and sits at the same table than if they
remain alone. First we must
measure the average amount of time people sit when they are alone.
This is the control condition and it gives us a baseline
against which to judge our results. Then
we send a confederate to sit at the same table and we measure the average
amount of time the person sits there.
This is the experimental
A control group, then, is
a group for whom the experimenter does not change the IV. The experimental and control groups must be matched on all important characteristics, e.g. age, sex, experience
Advantages of laboratory experiments:
Experiments are the only means by which cause
and effect can be established. It
has already been noted that an experiment differs from non-experimental
methods in that it enables us to study cause and effect because it
involves the deliberate manipulation of one variable, while trying to keep
all other variables constant. Sometimes
the independent variable (IV) is thought of as the cause and the dependent
variable (DV) as the effect.
It allows for precise control
of variables. The
purpose of control is to enable the experimenter to isolate the one key
variable which has been selected (the IV), in order to observe its effect
on some other variable (the DV); control is intended to allow us to
conclude that it is the IV, and nothing else, which is influencing the DV.
Experiments can be replicated.
We cannot generalise from the results of a single experiment.
The more often an experiment is repeated, with the same results
obtained, the more confident we can be that the theory being tested is
valid. The experimental
method consists of standardised procedures and measures which allow it to
be easily repeated.
It is also worth noting that an experiment yields quantitative data
(numerical amounts of something) which can be analysed using inferential
statistical tests. These
tests permit statements to be made about how likely the results are to
have occurred through chance.
Limitations of laboratory experiments:
The experiment is not typical of real life situations.
Most experiments are conducted in laboratories - strange and
contrived environments in which people are asked to perform unusual or
even bizarre tasks. The artificiality of the lab, together with the 'unnatural'
things that the subjects may be asked to do, jointly produces a distortion
of behaviour. Therefore
it should be difficult to generalise findings from experiments because
they are not ecologically valid (true to real life).
Behaviour in the laboratory is very narrow in its range.
By controlling the situation so precisely, behaviour may be very
A major difficulty with the experimental method is demand characteristics. Some
of the many confounding variables in a psychology experiment stem from the
fact that a psychology experiment is a social
situation in which neither the Subjects or the Experimenters are
passive, inanimate objects but are active, thinking human beings.
Imagine you’ve been asked to take part in a psychology
experiment. Even if you didn’t study psychology, you would be trying to
work out what the experimenter expected to find out. Experimenters too have expectations about what their results
are likely to be. Demand characteristics are all the cues which convey to the participant
the purpose of the experiment.
The experimental method as used in psychology has a history of
using biased or unrepresentative
sampling. George Miller
(1962) estimated that 90% of U.S. experiments have used college students
(who are accessible and 'cheap') and yet the results still tend to be
generalised to the U.S. population as a whole, and often beyond that to
Britain, Western Europe, etc. But
there is no reason to believe that U.S. college students are typical of
any other group in terms of gender, age, personality, social class
background or any other subject variable which can influence how subjects
will perform in any experimental situation.
What's more, these students are often psychology students who are
required to participate in research as a course requirement!
It has already been noted that a strength of the experimental
method is the amount of control which experimenters have over variables. However it must also be noted that it is not possible to
completely control all variables. There
may be other variables at work which the experimenter is unaware of.
In particular, it is impossible to completely control the mental
world of people taking part in a study.
A very major problem with the experimental method concerns ethics. For example,
experiments nearly always involve deceiving participants to some extent
and the very term 'subject' implies that the participant is being treated
as something less than a person. Recently the use of the experimental
method has come under considerable criticism for the way that researchers
often break ethical guidelines. It
is also important to recognise that there are very many areas of human
life which cannot be studied using the experimental method because it
would be simply too unethical to do so.
Another issue is to do with normative data.
Some researchers consider that an important advantage which
experiments have over, say, observational techniques is the random
assignment of research participants to experimental conditions.
This helps to reduce the problems of analysis caused by systematic
differences between people. Other
psychologists, however, argue that grouping people together in this way,
and trying to cancel out individual differences so that we only look at a
group norm, is limited in how much it can tell us because it ignores what
is special about people.
Mainly because of the
above limitations psychologists are increasingly more likely to use other
non-experimental methods - and in particular more qualitative methods.
The Field Experiment:
Sometimes it is possible
to carry out experiments in a more natural setting, i.e. in ‘the field
’. A famous example of this
is the series of studies carried out by Piliavin et al (1969) in which
they arranged for a person to collapse on an underground train and waited
to see how long it was before the person was helped.
One of the independent variables they used was the appearance of
the ‘victim’: whether he
was carrying a walking stick or whether he appeared to be drunk.
As with the laboratory
experiment, the independent variable is still deliberately manipulated by
However it is not possible
to have such tight control over variables in the field, but it does have
the advantage of being far less artificial than the laboratory.
In some circumstances,
psychologists can take advantage of a natural situation in order to carry
out an investigation in circumstances which they cannot themselves
manipulate. For example, a
primary school may decide to try out a completely new reading scheme and
the effects of this could be compared with a similar school using a
different reading scheme. A
local hospital may decide to have mixed wards rather than separate wards
for men and women. The effects on the patients of being in these wards could be
compared with those in single-sex wards.
This is not a true
experiment because the psychologist is unable to manipulate or control
variables. For this reason it
is sometimes referred to as a quasi-experiment.
It is possible, though to compare two groups, the equivalent of an
experimental and a control group. It
has the advantage that the participants are unaware that they are taking
part in an investigation and it is certainly not as artificial as a