Types of experiment

• Lab Experiments

  • Researcher manipulates IV to measure effect on DV
  • highly controlled
  • standardised procedure
  • PPS randomly allocated
• Natural experiments: IV is not manipulated as it will occur/change naturally. Extraneous variables are not measured or controlled. PPS not randomly allocated as they are pre-set. Researcher measures the natural change in the DV
• Field experiment:

  • Researcher manipulates IV to measure DV
  • Naturalistic setting
  • Extraneous variables can not be controlled - unpredictability of real-life, PPS not aware they are being studied.
  • Most of the time PPS not randomly allocated
• Quasi Experiment:

  IV) is based on an existing difference between people. It cannot be manipulated as it is innate and cannot be changed.

  • No control over extraneous variables or the environment.
  • Participants are NOT randomly allocated
• What is a strength of a lab experiment?

  Conclusions are clear and easy to make (compared to other methods) due to the high level of control the researcher is able to exert.
• what is a strength of a lab experiment?

  uses standardised procedure, the research is replicable, so reliability increases.
• What is a strength of lab experiment?

  High internal validity is achieved as the independent variable may be seen to affect the dependent variable with no interference from extraneous variables
• limitation of Lab experiments?

  Demand characteristics may be an issue as participants know they are in a study and so may alter their behaviour which impairs the validity of the study
• Limitation of Lab experiment?

  lacks ecological validity due to the artificial nature of the procedure
• limitation of lab experiment?

  lacks mundane realism (how an individual would act in day to day life) meaning the results cannot be generalised to real-world behaviour
• Strength of field experiment?

  Likely to have higher ecological validity than laboratory experiments, as the natural settings will relate to real life.
• Strength of field experiments

  participants are less likely to show demand characteristics as they are less likely to know what is expected from them and are often in their 'natural' environment.
• strength of field experiment

  High levels of mundane realism, which means the results are more likely to be able to be generalised to real-world behaviours
• Limitation of field experiment

  It is harder to control the extraneous variables in a natural environment. Therefore could confound results which makes it difficult to find truly causal effects between independent and dependent variables.
• limitation of field experiment

  Ethical principles have to be considered, such as the lack of informed consent; if participants are not made aware of their participation in an experiment, privacy must be respected during observations and participants must be debriefed appropriately when observations come to an end
• Limitation of field experiment

  Precise replication of the natural environment of field experiments is difficult, so they have poor reliability, unlike laboratory experiments where the exact conditions can be recreated.
• strength of natural experiment: The natural setting means that results will have high ecological validity (i.e. they should relate well to real life behaviour).
• Strength of Natural experiment:

  Demand characteristics are often not a problem,unlike laboratory experiments (i.e. participants are less likely to adjust their natural behaviour according to their interpretation of the study’s purpose, as they might not know they are taking part in a study).
• Strength of Natural Experiment:

  it can be used in situations in which it would be ethically unacceptable to manipulate the independent variable, e.g., researching stress.
• Limitation of Natural experiment:

  There is no control over extraneous variables that might bias the results. Makes it difficult for another researcher to replicate the study in exactly the same way.
• Limitation of natural experiment

  Being unable to randomly allocate participants to conditions means that sample bias may be an issue (e.g. other extraneous variables that change with the pre-set IV group differences may confound the results, meaning a causal IV-DV effect is unlikely).
• Limitation of natural experiment:

  Ethical issues such as lack of informed consent commonly arise, as deception is often required; debriefing, once the observation/experiment has ended, is necessary.
• Limitation of natural experiments:

  They may be more expensive and time-consuming than lab experiments.
• Strength of Quasi experiments:

  The natural setting means that results will have high ecological validity (i.e. they should relate well to real life behaviour).
• Strength of Quasi experiments?

  High ecological validity – due to the lack of involvement of the researcher; variables are naturally occurring so findings can be easily generalised to other (real life) settings, resulting in high external validity.
• Strength of Quasi:

  Only way to study factors that are pre-existing between participants.
• Limitation of Quasi Experiments:

  Lack of control – natural experiments have no control over the environment & other extraneous variables which means that the researcher cannot always accurately assess the effects of the I.V, so it has low internal validity.
• Limiation of quasi experiments

  Not replicable – due to the researcher’s lack of control, research procedures cannot be repeated so that the reliability of results cannot be checked.