Types of experiments

• Laboratory experiment: IV is manipulated to see the effects on the DV. Conducted in a highly controlled environment
• Strengths of laboratory experiment:

  • High control over variables
  • Allows us to draw conclusions that the IV caused a change in the DV
  • Have high internal validity
  • Replication is possible because of the high levels of control. This means we can check the validity of the results, and ensure they are not just a 'one-off'
• Weakness of laboratory experiment:

  • Lack of generalisability - the environment is artificial and not like everyday life. Participants may behave in unusual ways and therefore their behaviour cannot be applied beyond the laboratory setting (Low external validity)
  • Usually know they are being tested so they are subject to demand characteristics
  • The actual task they do is often unlike real life - this means they lack mundane realism
• Field experiment: IV is manipulated but in a more natural setting
• Strengths of field experiment:

  • Higher mundane realism because the tasks tend to be more like what they would do in everyday life. Also, less controlled so behaviour is more realistic
  • Often do not know they are being studied, so behaviour is more natural (high external validity)
• Weakness of field experiment:

  • Less controlled which means a higher chance of extraneous variables affecting the DV rather than just the IV. Makes it slightly more difficult to establish cause and effect
  • Replication not possible
  • Ethical issues are a problem - informed consent and privacy
• Natural experiment: the IV is not manipulated by the researcher. It simply has 'happened' and would have occurred whether the researcher would have been there. The researcher takes advantage of a pre-existing IV. It can be performed in a laboratory - it does not have to be a natural setting
• Strengths of natural experiment:

  • Provide opportunites for studies that would otherwise not be possible to research, mainly due to ethical reasons
  • High external validity - real life situations with no manipulation
• Weakness of natural experiment:

  • Naturally occurring events happen rarely, which limits the scope for research
  • Rare events mean it is difficult to generalise findings to other similar situations
  • Participants cannot be randomly allocated to conditions which means we can be less sure of whether it was the IV affecting the DV
• Quasi experiment: These have an IV that is based on an existing difference between people
• Strength of quasi experiments:

  Quasi experiments are often carried out under controlled conditions and therefore share some strengths of a laboratory experiment
• Weakness of quasi-experiment:

  • Quasi experiment, like natural experiments, cannot randomly allocate participants to conditions and therefore there may be confounding variables
  • In addition, both quasi-experiments and natural experiments, the IV is not deliberately changes by the researcher and therefore we cannot claim that the IV has caused any observed change
• Internal validity is about what goes on inside an experiment. Refers to how controlled the study is. If we have controlled as many extraneous variables as possible, it will have high internal validity
• External validity is about generalising the findings from a study to other situations, such as everyday life. Refers to the degree to which research findings can be generalised to the wider population. That is the whole point of doing research
• There are 3 different types of external validity:

  • Ecological validity - other settings
  • Population validity - other types of people
  • Temporal/historical validity - over different periods of time
• Mundame realism: the task in the experiment LACKS mundame realism if it is unlike real life
• Generalisable: the extent to which findings (from a study) can be generalised (or extended) to those in natural settings