A Level Psychology at Spalding Grammar School

The most powerful tool in the Scientist's kit box is the experimental method. The classic LAB EXPERIMENT involves controlling all the variables in a particular environment. The participants are split into two groups. One group, the CONTROL GROUP, caries out a task in the controlled environment. Another group, the EXPERIMENTAL GROUP, carries out the same task but one crucial variable has been changed - this is the INDEPENDENT VARIABLE. The researcher measures the outcome and any difference between the control group and the experimental group must be down to the Independent Variable (I.V.).

This method is based on what researchers do in the physical sciences (chemistry, physics, etc). There is some debate about whether this method works well with human beings, who may be aware they are being experimented on and react to it in unpredictable ways. There are several variations on the classic lab experiment:

• FIELD EXPERIMENTS: These are carried out in a real-life setting, often with real people who don't realise they're in an experiment. The great advantage is realism: the researcher can be sure he's seeing natural behaviour. The problem is the lack of control: you can't control a field setting the way you can a laboratory environment so all sorts of things can interrupt or interfere with the experiment; that's why you can't be sure the I.V. alone is causing the results.
• NATURAL (or QUASI-) EXPERIMENTS: These investigate a naturally-occurring variable, something like hair colour, race, gender or occupation. Unlike a lab experiment, you can't assign participants to the control group or experimental group fairly: in effect, the participants arrive in those groups. This means you can't be quite sure that the two groups were otherwise the same, so you can't be certain that the I.V. was responsible for the results.