Types of experiment

• Laboratory experiment


  An experiment which takes place in a controlled environment within which the researcher manipulates the IV and records the effect on the DV, whilst maintaining strict control of extraneous variables.
• Strengths of laboratory experiment

  • High control over confounding variables and extraneous variables. Any effect on the DV is likely to be as a result of manipulation of the IV. So we can establish cause and effect (high internal validity)
  • Replication is possible, due to high level of control. This ensures that new extraneous variables are not introduced when repeating an experiment. This is important as it checks whether results are valid.
• Limitations of laboratory experiment

  • Lack generalisability, due to artificial environment in the lab. In an unfamiliar environment participants may behave in different ways, low external validity. Participants are also aware they are being studied which may rise demand characteristics.
  • Low mundane realism, tasks participants carry out may not represent usual everyday experiences.
• Field experiment


  An experiment which takes place in a natural setting within which the research manipulates the IV and measures the effect on the DV.
• Strengths of field experiments

  • High mundane realism, environment is more natural so behaviour produced may be more valid and authentic, so high external validity.
• Limitations of field experiments

  • Loss of control of CVs and EVs. This means causes and effect between IV and DV may be more difficult to establish and precise replication is not always possible.
  • Ethical issues, if participants are unaware they are being studied they cannot consent and research may constitute an invasion of privacy.
• Natural experiment

  An experiment where the change in IV is not brought about by the researcher, but would have happened even if the researcher was not there. The researcher records the effect on a DV they have decided on.

  e.g before a natural disaster.

  IV is natural, not necessarily the setting, participants may still be tested in a lab.
• Strengths of a natural experiment

  • Provide opportunities for research that may not otherwise be undertaken for practical and ethical reasons. E.g studying Romanian orphans.
  • High external validity because they involve the study of real life problems as they happen. E.g the effects of a natural disaster on stress levels.
• Limitations of a natural experiment

  • A naturally occurring event may occur rarely, reducing opportunities for research, limits scope for generalising findings to other situations.
  • Participants may not be randomly allocated to different experimental conditions. Researcher may be less sure if the IV has caused changes in the DV.
  • Research can be conducted in a lab, may lac realism and demand characteristics may be an issue.
• Quasi experiment

  A study that is almost an experiment. The IV has not been determined by anyone, the variables simply exist. E.g being old or young.
• Strength of quasi experiment

  • Quasi experiments are often carried out in controlled conditions, so share strengths of lab experiment e.g replication.
• Limitations of quasi experiment

  • Quasi experiments like natural experiments cannot randomly allocate participants to conditions there may be confounding variables.
  • In addition in both quasi and natural experiments the IV is not deliberately changed by the researcher, therefore we cannot claim that the IV has caused any observed change.