Types of Experiments

• What are laboratory experiments?

  Laboratory experiments are conducted in highly controlled environments. This is not always a laboratory (lab) - it could, for example, be a classroom where conditions can be well-controlled.
• What are the strengths of laboratory experiments? (part 1)

  • High control over confounding variables (CVs) and extraneous variables (EVs) - allows researcher to ensure that any effect on the dependent variable (DV) is likely to be the result of manipulation of the independent variable (IV) - makes us more certain about demonstrating cause and effect (high internal validity).
• What are the strengths of laboratory experiments? (part 2)

  • Replication is more possible than in other types of experiment because of the high level of control - ensures that new EVs are not introduced when repeating an experiment - this is vital to check the results of any study to see whether the finding is valid and not just a one-off.
• What are the limitations of laboratory experiments? (part 1)

  • May lack generalisability - lab environment may be rather artificial and not like everyday life, an unfamiliar context may cause participants to behave in unusual ways so their behaviour cannot always be generalised beyond the research setting (low external validity).
• What are the limitations of laboratory experiments? (part 2)

  • More demand characteristics - participants are usually aware they're being tested in a lab experiment which may give rise to ’unnatural’ behaviour.
  • Low mundane realism - tasks participants are asked to carry out in a lab experiment may not represent everyday experience e.g. recalling unconnected lists of words as part of a memory experiment.
• What are field experiments?

  In field experiments the IV is manipulated in a natural, more everyday setting (in the field). The researcher goes to the participant’s usual environment rather than, in a lab experiment, participants going to a researcher’s lab.
• What are the strengths of field experiments?

  • Higher mundane realism - environment is more natural thus potentially producing behaviour that is more valid and authentic - especially the case as participants may be unaware they're being studied (high external validity).
• What are the limitations of field experiments?

  • Loss of control of CVs and EVs (due to increased realism) - this means cause and effect between the IV and DV in field situations may be much more difficult to establish and precise replication is often not possible.
  • Ethical issues - if participants are unaware they’re being studied they cannot consent to being studied and such research might constitute an invasion of privacy.
• What are natural experiments?

  An experiment where the change in the IV is not brought about by the researcher, but would have happened even if the research had not been there. The researcher records the effect on the DV. It is the IV that is natural, not necessarily the setting - participants may be tested in a lab.
• What are strengths of natural experiments?

  • Provide opportunities for research that may not otherwise be undertaken for practical or ethical reasons e.g. the studies of institutionalised Romanian orphans.
  • High external validity - involve the study of real-world issues and problems as they happen e.g. the effects of a natural disaster on stress levels.
• What are the limitations of natural experiments? (part 1)

  • Loss of control - IV is not directly manipulated by the experimenter therefore the degree of control is inevitably less than in either a lab/field experiment - reduces likelihood of cause and effect being established.
  • Likelihood of the desired behaviour being displayed - the naturally occurring IV that the researcher wishes to study may occur only rarely, thus reducing the available opportunities for research.
• What are quasi experiments?

  A study that’s almost an experiment but lacks key ingredients. The IV has not been determined by anyone - the variables simply exist e.g. being old or young.
• What are strengths of quasi experiments?

  • Often carried out under controlled conditions and therefore share some strengths of a laboratory experiment e.g. replication (control of EVs).
  • Allows comparisons between different types of people.
• What are limitations of quasi experiments?

  • (Like natural experiments,) cannot randomly allocate participants to conditions and therefore there may be CVs.
  • IV is not deliberately changed by the researcher and therefore we cannot claim that the IV has caused any observed change.