The prime method of enquiry in science is the experiment. The key features of the experiment are control over variables (independent and extraneous), careful measurement, and establishing cause and effect relationships (between IV and DV).
Therefore, an experiment is:
“An investigation in which the independent variable is manipulated (or changed) in order to cause a change in the dependent variable”
There are three mains types of experiments:
This type of experiment is conducted in a well-controlled environment – not necessarily a laboratory – and therefore accurate measurements are possible. The researcher decides where the experiment will take place, at what time, with which participants, in what circumstances and using a standardised procedure. An example is Asch’s experiment on conformity or Milgram’s experiment on obedience.
• Pro: It is easier to replicate (i.e. copy) a laboratory experiment.
• Pro: They allow for precise control of extraneous and independent variables.
• Pro: They allow cause and effect relationships to be established.
o Con: The artificiality of the setting may produce unnatural behaviour that does not reflect real life, and results cannot be generalised to the population.
o Con: Demand characteristics may bias the results and become confounding variables.
Field experiments are done in the everyday (i.e. natural) environment of the participants but the situations are still artificially set up. The experimenter still manipulates the IV, but in a real-life setting (so cannot really control extraneous variables), e.g. Sherif’s Robbers Cave.
• Pro: Behaviour in a field experiment is more likely to reflect life real because of it natural setting, i.e. higher ecological validity than a lab experiment.
• Pro: There is less likelihood of demand characteristics affecting the results, as participants may not know they are being studied.
o Con: There is less control over extraneous variables that might bias the results. This in turn makes the experiment harder to replicate.
o Con: They may be more expensive and time consuming than lab experiments.
Natural experiments are conducted in the everyday (i.e. natural) environment of the participants but here the experimenter has no control over the IV as it occurs naturally in real life, e.g. Hodges and Tizard's research (1989) which compared the long term devlopment of children who have been adopted, fostered or returned to their mothers with a controkl group of children who had spent all their lives in their biological families.
• Pro: Behaviour in a natural experiment is more likely to reflect life real because of it natural setting, i.e. very high ecological validity.
• Pro: There is less likelihood of demand characteristics affecting the results, as participants may not know they are being studied.
• Pro: Can be used in situations in which it would be ethically unacceptable to manipulate the independent variable.
o Con: There is less control over extraneous variables that might bias the results. This in turn makes the experiment harder to replicate.
o Con: They may be more expensive and time consuming than lab experiments.
o Ecological validity: The degree to which an investigation represents real-life experiences.
o Demand characteristics: the clues in an experiment that lead the participants to think they know what the researcher is looking for (e.g. experimenters body language etc).