Research Methods - AS


The experimental method

Three main types of experimental method

  • Laboratory experiments
  • Field experiments
  • Natural experiments


  • Independent Variable: This is what the researcher manipulates. Often a researcher will look at how participants react in two different situations. Therefore, they will manipulate the situation so that it is different on two occasions. It is assumed that the IV will have a direct effect on the dependent variable (DV).
  • Dependent variable: This is what the researcher measures (the change in behaviour). A researcher will look at how behaviours change as a result of the manipulation of the IV.
  • Extraneous Variables: There are any varaibles other than the IV that might affect the DV. an example of this could be temperature. It is important the researchers consider potential extraneous variables, and try to control them.
  • Confounding Variables: Occasionally some extraneous variables cannot be controlled (e.g. if the heating system was broken). These then become confounding variables.
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The experimental method

Advantages of the experimental method as a whole are:

  • East to replicate due to the high level of control experimenters have. This means that others can carry out the experiment as it was carried out oringinally in order to check the reliability of the results. iIf the same results are found time and time again, the orginal findings are said to be reliable.
  • The high degree of control experimenters have over all variables means that casual relationships can be inferred. We can usually be sure that changes observed in the dependent variable are due to changes in the independent varaible.

Disadvantages of the experimental method as a whole are:

  • The experimental situation is often very artifical. This means the findings cannot necessarily be generalised to real life situations. We call this low ecological validity.
  • Usually participants know that they are taking part in an experiment. This factor alone could cause changes in the DV. Often pps will try to guess the aim of the experiment and either change their behaviour to fit in with what they think the experimenter wants or change their behaviour against what they think the experimenter wants know as the 'screw you effect'. When a pps changes their behaviour in response to their perception of what they think is required it is known as demand characteristics.
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Laboratory Experiments

The laboratory experiment is the most scientific method available to psychologists. This is because it involves the highest level of control over all variables. Laboratory experiments aare tose that take place in a controlled environment. The idea is that all exraneous variables can be controlled so that any cahnges in the DV can be said to be due to changes in the IV.

Advantages of Lab experiments

  • Easy to replicate - due to high degree of control lab experiments are extremely easy to replicate. Therefore, it is easy to test reliability of the orginal findings.
  • High degree of control - As extraneous variables are so well controlled, it is easy to assume that cahanges in the DV are due to chnages in the IV.

Disadvantages of Lab experiemnts

  • Low ecological validity - It might be difficult to generalise to real world situations as the experiment situation is so artifical.
  • Demand Characteristics - pps may change their behaviour to fit with what they believe the experimenter does or doesnt want.
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Field Experiment

Field experiment still involve manipulation of an IV in order to measure its effects on the DV. The only difference is the location of the experiment. Whilst lab experiments are carried out in the researchers' environment, field experiments are carried out in the pps natural environment. This means we are measuring behaviour in the location in which it would normally occur.

Advanatges of field experiments

  • High ecological vailidty - field experiments have much higher ecological validity than laboratory experiments because they are conducted in the participants' own environment. Therefore we can be fairly confident that the participants are acting as they normally would.
  • Cause and effect can still be inferred - Field experiment still involve the manipulation of the IV in order to see the effects on the DV, and so we can still be fairly confident that any changes in the DV are due to changes in the IV.
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Field experiment

Disadvantages of Field experiemnt

  • Less control - researchers have a lot less control over extraneous varaibles in field experiments. Therefore the cause and effect relationship between the IV and DV is not as strong as in the lab experiment.
  • Potential ethical issues - Often pps don't known that they are taking part in the study. This is considered unethical as participants are meant to give their consent to the researchers prior to the study.
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Natural experiment

In natural experiments, the IV s not directly manipulated by the researcher, it is something that was going to change anyway. This is a type of quasi-experiment (not a 'true' experiment).

Advantages of natural experiments 

  • High ecological validity: This experimental method has the highest level of ecological validity as the independent variable is not manipulated at all by the researchers. Participants are acting as they would naturally, it just happens to be that researchers are there to measure their behaviour.
  • Sometimes it is the only possible method: It is often not possible to manipulate the independent variable. In such cases natural experiments provide the only opportunity to study the behaviour in question. 

Difficult to replicate: Often changes in the IV are 'one offs' and so the reliability of the results cannot be tested through replication

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Natural experiment

Disadvantages of natural experiments 

  • Difficult to replicate: Often changes in the IV are 'one offs' and so the reliability of the results cannot be tested through replication. 
  • Lack of control: As the IV is not being directly manipulated by the researchers there is less control in the natural experiment as compared to the laboratory experiment.
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Non experimental methods

A non experimental method is one which doesn't have an independent variable. No variables are directly controlled in these methods.

There are five main types of non experimental method available to psychologists:

  • Correlational Analysis 
  • Observation
  • Self report techniques: This is where pps provide information knowingly about specific things relating to themselves, as opposed to the researche observing these things directly. There are two sel report techniques:  -Questionnaire   - interview 

Case studies: You will need to be able to describe/recognise each of these methods, consider the strengths and limitations of each method, and be able to describe how you would go about carrying out a study using these methods.

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