Experimental methods

• Experimental methods aim to find a cause and effect relationship between an independent variable and a dependent variable, and to measure the extent of this effect.
• Laboratory experiments are conducted under specified controlled conditions in which the researcher manipulates the independent variable to measure the effect on the dependent variable.
• The conditions in laboratory experiments are heavily controlled to minimise the effect of any extraneous variables, preventing them from becoming confounding variables which might adversely affect the dependent variable.
• Participants in laboratory experiments are aware that they are taking part in an investigation due to the contrived nature of the situation, which may feel unlike real life.
• A strength of laboratory experiments is the high degree of control over extraneous variables which can be achieved, allowing for conclusions about cause and effect to be drawn between the independent variable and the dependent variable. Therefore they have had high internal validty
• A limitation of laboratory experiments is that they can lack external validity due to the artificial nature of the environment in which the investigation is taking place, meaning the study may lack ecological validity and the findings cannot always be generalised to settings beyond the laboratory.
• Demand characteristics can be seen in field experiments due to participants knowing they are being investigated.
• Field experiments are carried out in natural conditions, in which the researcher manipulates the independent variable to measure the effect on the dependent variable, high ecological validty
• The 'field' in field experiments is considered any location which is not a laboratory.
• In field experiments, participants' behaviour is typically not influenced by the fact that they are taking part in an investigation, resulting in more natural observations.
• The natural setting of field experiments often results in a higher level of ecological validity, meaning the results are more likely to be representative of behaviour witnessed in everyday life.
• A strength of using natural experiments is the unique insights gained into real-life situations from using this methodology.
• The independent variable (IV) in a natural experiment is naturally occurring, such as a flood or earthquake, and the behaviour of people affected is either compared to their own behaviour beforehand, when possible, or with a control group who have not encountered the IV.
• In a natural experiment, the researcher does not manipulate the independent variable (IV) and instead examines the effect of an existing IV on the dependent variable (DV).
• There is less control over extraneous variables in field experiments, which can then become confounding variables and distort the findings, meaning a firm cause and effect relationship cannot be drawn since other factors could have had an impact on the dependent variable, other than the independent variable.
• Since the independent variable (IV) in a quasi-experiment is a naturally occurring difference between the participants, the level of IV to which they belong is pre-decided.
• Quasi-experiments do not have to be conducted in a natural setting, although they often are.
• Quasi-experiments contain a naturally occurring independent variable (IV), but one which already exists.
• When quasi-experiments take place under natural conditions, there is no control over the environment and subsequent extraneous variables, making it difficult to be sure that factors such as age, gender or ethnicity have affected the dependent variable (DV).
• Natural experiments often have a higher level of external validity, compared to laboratory and field experiments due to the naturally occurring independent variable (IV).
• A limitation of quasi-experiments is that participants cannot be randomly allocated to research conditions to remove the issue of bias in the procedure.
• A naturally occurring event that interests researchers may only occur very rarely, limiting the opportunity to generalise the results to other similar events or circumstances.
• The researcher examines the effect of this independent variable (IV) on the dependent variable (DV) in a quasi-experiment.
• Natural experiments have high levels of ecological validity because they examine real-world issues in a natural setting.
• Investigating a naturally occurring independent variable (IV) allows for research to be conducted into areas of psychology that could not be generated for ethical reasons or because of logistical and practical constraints.
• Natural experiments have no control over the environment and subsequent extraneous variables, which means that it is difficult for the research to accurately assess the effects of the independent variable (IV) on the dependent variable (DV).
• There are important ethical issues associated with field experiments as participants are often unaware that they are, in fact, participants in a psychological investigation, meaning their privacy rights may be violated and a cost-benefit analysis will need to be conducted before proceeding with any study to ensure the perceived outcomes from the research will outweigh any personal costs to those involved.
• Quasi-experiments allow researchers to compare different types of people easily to provide insight into similarities or differences between these groups which could not be ethically generated otherwise.
• There are methodological issues associated with conducting quasi-experiments.
• Quasi-experiments may also be conducted in a laboratory setting, under controlled conditions.
• A limitation of quasi experiments is that participants cannot be randomly allocated to research conditions to remove the issues of bias in the procedure. Since the IV is a naturally occurring difference between the participants, the live of the IV to which they belong to is pre-decided. This means the psychologist will be less certain that the independent variable (IV) alone will have caused the effect which is measured through the dependent variable (DV), as other dispositional or environmental factors may have played a role in the outcome.
• Natural experiments are a type of field experiment in which the independent variable is not manipulated by the researcher, but rather, occurs naturally.
• Natural experiments are conducted in natural conditions, with participants unaware that they are taking part in an investigation, resulting in more natural observations.
• The natural setting of natural experiments often results in a higher level of ecological validity, meaning the results are more likely to be representative of behaviour witnessed in everyday life.
• There is less control over extraneous variables in natural experiments, which can then become confounding variables and distort the findings, meaning a firm cause and effect relationship cannot be drawn since other factors could have had an impact on the dependent variable, other than the independent variable.
• There are important ethical issues associated with natural experiments as participants are often unaware that they are, in fact, participants in a psychological investigation, meaning their privacy rights may be violated and a cost-benefit analysis will need to be conducted before proceeding with any study to ensure the perceived outcomes from the research will outweigh any personal costs to those involved.