types of experiment

• laboratory experiment

  • A controlled environment where extraneous and confounding variables can be regulated
  • Participants go to researcher
  • The IV is manipulated and the effect on the DV is recorded
• laboratory experiment evaluation

  • Strength = EVs and CVs can be manipulated:
  • this means that the effect of EVs and CVs on the DV can be minimised
  • Cause and effect between the IV and DV can be demonstrated => high internal validity
  • Strength = can be easily replicated
  • Greater control means less chance that new EVs can be introduced
  • Means that findings can be con firmed, supporting their validity
  • Limitation = lack generalisability
  • Controlled lab experiment = artificial and pps aware they are being studied
  • => behaviour not natural so cant be generalised to everyday life, low external validity
  • limitation = demand characteristics
  • Cues in the experimental situation that invited a particular repsonse from pps
  • Findings mat be explained by these cues rather than the effect of the IV (lower internal validity)
• field experiment

  • A natural setting
  • The researcher goes to participants
  • The IV is manipulated and the effect on the DV is recorded
• field experiment evaluation

  • Strength = more natural enviornament
  • pps more comfortable => behaviour more authentic
  • Results may be more generalisable to everyday life
  • Strength = pps are unaware of being studied
  • They are more likely to behave as they normally do so the findings can be generalised
  • Study has greater validity
  • Limitation = more difficult to control CVs/EVs
  • Observed changes in the DV may not be due to the IV
  • => more difficult to establish cause and effect in the lab
  • Limitation = ethical issues
  • pps in a field experiment may not have given informed consent
  • => invasion of pps privacy
• natural experiment

  • The experimenter does not manipulate the IV (it does change, but the change is not made by the experimenter) someone or something else causes the IV to vary
  • The IV would have varied even if the experimenter wasn't interested
  • DV may be naturally occurring (eg. exam results) or may be devised by the experimenter and measured in the field or a lab
• Natural experiment evaluation

  • Strength = may be only practical/ethical option
  • May be unethical to manipulate the IV (eg studying the effects of institutionalisation on children)
  • Natural experiment may be only way causal research can be done on such topics
  • Strength = greater external validity
  • Natural experiments involve real world issues (eg effects of natural disasters on stress levels)
  • Means findings are more relevant to real experiences
  • Limitation = natural event may only occur rarely
  • Many natural events are ‘one-offs’ and this reduces the opportunity for research
  • May limit the scope for generalising findings to other similar situations
  • Limitation = pps not randomly allocated
  • Experimenter has no control over which pps are placed in which condition as the IV is pre-existing
  • May result in CVs that aren’t controlled (eg Romanian orphans adopted early may also be the friendlier ones)
• quasi-experiment

  • IV is based on a pre-existing difference between people (eg age or gender)
  • No one has manipulated this variable, it simply exists
  • DV may be naturally occurring (eg exam results) or may be devised by the experimenter and measured in the field or a lab
• Quasi-experiment evaluation

  • Strength = often high control
  • Often carried out under controlled conditions and => shares cone of the strengths of lab experiments
  • Means replication is possible (for example)
  • Strength = comparisons can be made between people
  • In quasi experiment = the IV is a difference between people (eg people with and without people)
  • Means comparisons between different types of people can be made
  • Limitation = pps not randomly allocated
  • Experimenter has no control over which pps 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
  • Limitation = causal relationships are not demonstrated
  • The research does not manipulate/control the IV (like natural experiment)
  • We cannot say for certain that any change in the DV was due to the IV