types of experiment

• Laboratory experiments - An experiment that takes place in a highly 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 lab experiments:

  • High control over extraneous variables - higher confidence IV is affecting the DV (high internal validity)
  • Easy to replicate due to controlled conditions - more reliable
• Limitations of lab experiments:

  • Lack generalisability because the lab environment may be artificial and not like everyday life and the tasks pps carry out may not represent real-life experiences. participants may act differently in this unfamiliar context and so their behaviour cannot always be generalised beyond the research setting (low external validity)
  • Participants are usually aware they are being observed/tested so there is a higher risk of demand characteristics
• Field experiments - An experiment that takes place in a natural setting within which the researcher manipulates the IV and records the effect on the DV
• Strengths of field experiments:

  • Higher mundane realism than lab experiments because the environment is more natural so they may produce more valid and authentic behaviour, especially if pps are unaware they are being studied (high external validity)
• Limitations of field experiments:

  • Loss of control of extraneous variables so cause and effect between the IV and the DV is much more difficult to establish (low internal validity)
  • Ethical issues. If pps are unaware they are being studied there is a lack of consent and such research may constitute an invasion of privacy
• Natural experiments - An experiment where the change in the IV is not brought about by the researcher but would have happened even if the researcher had not been there. The researcher records the effect on the DV. They take advantage of a pre-existing IV
• Strengths of natural experiments:

  • Allows research to be carried out that otherwise may not be undertaken for practical or ethical reasons e.g Rutter’s study on institutionalised Romanian orphans
  • Often have high external validity because they involve the study of real-life issues as they happen such as the effects of natural disasters on stress levels
• Limitations of natural experiments:

  • Reduced opportunities for research as it has to be naturally occurring
  • limited generalisability
  • pps may not be randomly allocated to experimental conditions. This means the researcher has less confidence that the IV affected the DV. (lower internal validity)
• Quasi-experiments - A study that is almost an experiment but lacks key ingredients. The IV has not been determined by anyone - the ‘variables’ simply exist such as being young or old. IV is based on an existing difference between people so no one has manipulated the IV
• Strengths of quasi experiments:

  • Often carried out under controlled conditions so have high control over extraneous variables and a high level of replication. (high internal validity)
• Limitations of quasi experiments:

  • Cannot randomly allocate participants to conditions and so there may be confounding variables