type of experiment

• The four types of experiment

  1. laboratory
  2. field
  3. natural
  4. quasi
• Laboratory experiments

  is where extraneous and confounding variables can be regulated. The participants go to the researcher, the IV is manipulated and the DV is recorded.
• Strengths of laboratory experiments

  1. EVs and CVs can be controlled. This means the effect of EVs and CVs on the DV can be minimised. Cause and effect between the IV and DV can be demonstrated meaning there will be as higher internal validity.
  2. It can be replicated easier. Greater control means there is less chance that new EVs are introduced. This means that findings can be confirmed, supporting their validity.
• Limitations of laboratory experiments


  1. It may lack generalisability. The controlled lab may be rather artificial and participants are aware of being studied. Therefore, behaviour may not be natural and can't be generalised to everyday life meaning it has low external validity.
  2. Demand characteristics may be a problem as there are cues in the experimental situation that invite a particular response from participants. The findings may be explained by these cues rather than the effect of the IV meaning there is lower internal validity.
• Field experiments

  occur in a natural setting. The researcher goes to participants, the IV is manipulated and the effect on the DV is recorded.
• Strengths of field experiments

  1. More natural environment. Participants are more comfortable and behaviour more authentic. Results may be more generalisable to everyday life.
  2. Participant are unaware of being studied. They are more likely to behave as they normally do so the findings can be generalised. The study has greater external validity
• Limitations of field experiments

  1. More difficult to control CVs/EVs. Observed changes in the DV may not be due to the IV, but to CVs/EVs instead. It is more difficult to establish cause and effect than in the lab.
  2. There are ethical issues. Participants in a field experiment may not have given informed consent. This is an invasion of participants' privacy, which raises ethical issues
• Natural experiment

  the experimenter does not manipulate the IV. It does change but it is caused by someone or something else. The IV would change even if the experimenter was not interested. DV may be naturally occurring (exam results) or may be devised by the experimenter and measured in the field or a lab.
• Strengths of natural experiments

  1. May be the only practical and ethical study. It may be unethical to manipulate the IV. A natural experiment may be the only way casual research can be done for such topics
  2. Greater external validity. Natural experiments involve real world issues, such as the effect of a natural disaster on stress levels. This means the findings are more relevant to real experiences.
• Limitations of natural experiments

  1. The natural event may only occur rarely. Many natural events are one offs and this reduces the opportunity for research. This may limit the scope for generalising findings to other similar situations
  2. Participants are not randomly allocated. The experimenter has no control over which participants are placed in which condition as the IV is pre existing. This may result in CVs that aren't controlled.
• Quasi experiment

  IV is based on a pre existing difference between people, e.g. age or gender. No one has manipulated this variable it just exists. DV may be naturally occurring or may be devised by an experimenter and measured in a field or a lab.
• Strengths of quasi experiments

  1. High control. Often carried out under controlled conditions and therefore shares some of the strengths of lab experiments. This means replication is possible.
  2. Comparisons can be made between people. In a quasi experiment the IV is a difference between people. This means that comparisons between people can be made.
• Limitations of quasi experiments

  1. Participants are not randomly allocated. The experimenter has no control over which participants are placed in which condition as the IV is pre existing. Participant variables may have caused the change in the DV acting as a CV.
  2. Causal relationships not demonstrated. As with a natural experiment, the researcher does not manipulate/control the IV. We cannot say for certain that any change in the DV was due to the IV.