types of experiments

• lab experiments

  Lab experiments are conducted under specified controlled conditions (not always a lab, could be any controlled environment such as a classroom) in which the researcher manipulates the IV to measure the effect on the DV.  The conditions are heavily controlled to minimise the effect of any extraneous variables to prevent them from becoming confounding variables which may adversely effect the DV. Participants will be aware that they are taking part in an investigations
• field experiment

  Field experiments are carried out in natural conditions, in which the researcher manipulates the IV to measure the effect on the DV. The ‘field’ is considered to be any location that is not a laboratory, this is usually in the field of interest. Participants in a field experiment typically do not know that they are taking part in an investigation, this is because researchers want to observe more natural behaviour.
• natural experiment 


  In a natural experiment, the researcher does not manipulate the IV and instead examines the effect of an existing IV on the DV. This IV is naturally occurring (such as a flood or earthquake) and the behaviour of people affected is either compared to their own behaviour beforehand of with a control group that have not encountered the IV. It is important to note that whist the IV is naturally occurring, participants could still be tested in a lab as part of the study. 
• quasi experiment

  Quasi experiments also contain a naturally occurring IV, but one that already exists, such as  a difference between people (gender, age, personality trait etc). The researcher examines the effect of this IV on the DV, quasi experiments do not have to be conducted in a natural setting, although they often are. They may also be conducted in a lab setting, under controlled conditions.
• lab experiment strengths

  • Lab experiments have high control over extraneous variables, this means that the researcher can be sure that the effect on the DV is likely to be a result of the manipulation of the IV. 
  • Replication is more possible because of the high level of control, replication is vital to check the results of any study to see whether the finding is valid (accurate), not just a one off.
• lab experiment limitations

  • Lab experiments may lack generalisability because the environment may be artificial and not like everyday life (participants may behave in unusual ways so their behaviour cannot always be generalised beyond the research setting – low external validity).
  • Demand characteristics may arise because they are aware that they are being tested.
  • Lacks mundane realism, the tasks given do not reflect real-life experiences.
• field experiment strengths

  • Field experiments have higher mundane realism than lab experiments because the environment is more natural.
  • Thus field experiments may produce behaviour that is more valid and authentic because they are usually unaware that they are taking part (high external validity).
• field experiment limitations

  • However, this realism means that there is a loss of control over extraneous variables. This mans cause and effect between the IV and DV is difficult to establish and precise replication is often not possible.
  • If participants are unaware they are being studies they cannot consent to being studied and the research might constitute an invasion of privacy (ethical issues).
• natural experiment strengths

  • Natural experiments provide opportunities for research that may not otherwise be undertaken for practical reasons.
  • Natural experiments often have high external validity because they involve the study of real-life issues and problems as they happen, such as the effects of a natural disaster on stress levels.
• natural experiment limitations

  • A naturally occurring event may only happen rarely, reducing the opportunity for research. 
  • Another issue is that participants may not be randomly allocated to experimental conditions (this only applies when there is an independent groups design). This means the researcher cannot be sure whether the IV affected the DV.
• quasi experiment strengths

  • Quasi experiments are often carried out under lab conditions and therefore share the strengths of a lab experiment:
  • Replication
  • Control over confounding variables.
• quasi experiment limitations

  • There are methodological issues associated with conducting quasi experiments, there is no control over the environment or any extraneous variables – making it difficult to be sure that factors such as age, ethnicity, gender have affected the DV. 
  • When quasi experiments take place under lab conditions, the high level of control means that the research often lacks ecological validity and the findings cannot always be generalised to real-life settings.