The Experimental Method


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 experimental method.

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 variables constant.


Experiments in the Laboratory:

In psychological 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 the researcher.

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 similar).


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 condition.


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 etc.


Advantages of laboratory experiments:


1.      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.


2.      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.


3.      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.


4.      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:


1.      Artificiality:  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).   


2.      Behaviour in the laboratory is very narrow in its range.  By controlling the situation so precisely, behaviour may be very limited. 


3.      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.


4.      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!


5.      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.   


6.      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.


7.      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 the researcher.

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.




Natural Experiments:


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 laboratory setting.