Types of experiment

• what are the four types of experiment?

  laboratory, field, natural and quasi-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.
• strengths of laboratory experiments

  1. EVs and CVs can be controlled. this means that the effects of EVs and CVs on the DV can be minimised. cause and effect between the IV and DV can be demonstrated (high internal validity).
  2. can be easily replicated. due to the standardised procedure the experiment can be repeated. if the results are the same this confirms their validity.
• limitations of laboratory experiments

  1. may lack generalisability. the controlled lab environment may be rather artificial and participants are aware they are being studied. thus behaviour may not be 'natural' and can't be generalised to everyday life (low external validity).
  2. demand characteristics may be a problem. these are cues in the experimental situation that invite a particular response from participants. the results of the experiment may be explained by these cues rather than the effect of the IV.
• field experiment

  a natural setting.

  the researcher goes to participants.

  the IV is manipulated and the effect on the DV is recorded.
• strengths of laboratory experiments

  1. more natural environment. participants more comfortable in their own environment. results may be more generalisable to everyday.
  2. participants are unaware of being studied. they are more likely to behave as they normally do so the findings can be generalised. the study has greater external validity.
• limitations of laboratory experiments

  1. more difficult to control CVs. observed changed in the DV may not be due to the IV, but to CVs instead. it is more difficult to establish cause and effect than in the lab.
  2. there are ethical issues. participants in a field experiment may not have given informed consent. this is an invasion of participants' privacy, which raises ethical issues.
• natural experiment

  the experimenter does not manipulate the IV. the IV would have varied even if the experimenter wasn't interested.

  DV may be naturally occurring (e.g. exam results) or may be measured by the experimenter.
• strengths of natural experiments

  1. may be the only ethical option. it may be unethical to manipulate the IV, e.g. studying the effects of institutionalisation on children. a natural experiment may be the only way casual research can be done for such topics.
  2. greater external validity. natural experiments involve real-life issues, such as the effect of a natural disaster on stress levels. this means the findings are more relevant to real experiences.
• limitations of natural experiments

  1. the natural event may only occur rarely. many natural events are 'one-offs' and this reduces the opportunity for research. this may limit the scope for generalising findings to other similar situations.
  2. participants are not randomly allocated. the experimenter has no control over which participants are placed in which conditions as the IV is pre-existing. may result in CVs that aren't controlled, e.g. Romanian orphans adopted earlier may also be the friendlier ones.
• quasi-experiment

  IV is based on a pre-existing difference between people, e.g. age or gender. no one has manipulated the variable, it simply exists.

  Dv may be naturally occurring (e.g. exam results) for may be measured by the experimenter.
• strengths of quasi-experiments

  1. there is often high control. often carried out under controlled conditions and therefore shares some of the strengths of lab experiments. this means increased confidence about drawing causal conclusions.
  2. comparisons can be made between people. in a quasi-experiment the IV is a difference between people, e.g. people with and without autism. this means that comparisons between different types of people can be made.
• limitations of quasi-experiments

  1. participants are not randomly allocated. the experimenter has no control over which participants 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.
  2. causal relationships not demonstrated. the researcher does not manipulate/control the IV. we cannot say for certain that any change in the DV was due to the IV.