Strengths and weaknesses of the experimental method

• Laboratory experiments are conducted in a laboratory setting where extraneous variables can be controlled.
• The Independent Variable (IV) can be manipulated and the Dependent Variable (DV) is measured.
• Participants (Pp’s) in laboratory experiments know they are taking part in an experiment even if they do not know the true aim of the research.
• Loftus and Palmer conducted a lab experiment to investigate the effect of Leading Questions on Estimations of Speed.
• Laboratory experiments are the most scientific of all experiments conducted in a laboratory setting where extraneous variables can be controlled.
• Standardised procedures allow for replication of research, which increases both the external reliability and the internal validity of the research findings.
• Lab experiments can be low in ecological validity, meaning results cannot always be generalised to everyday behaviours.
• Field experiments are conducted in a more natural environment such as schools, hospitals etc.
• In field experiments, the Independent Variable (IV) is manipulated but participants may not always know they are taking part in an experiment.
• Langer and Rodin conducted a field experiment to investigate if elderly residents living in a care home were given greater choice would it affect alertness and activity.
• Field experiments are high in ecological validity.
• Quasi Experiments can be conducted in the lab or in the field.
• In Quasi Experiments, the Independent Variable (IV) is not manipulated it occurs naturally.
• Raine conducted a Natural Experiment to investigate if murderers pleading not guilty by reason of insanity have different brain functioning to non murderers.
• Raine’s research was conducted in a lab using scientific equipment.
• A weakness of laboratory experiments is that results can be affected by demand characteristics as the participants know that they are taking part in research and may try to guess the aim. Trying to guess the aim can unconsciously change behaviour so that they behave in a way they think the researcher wants them to. This can invalidate the results.
• A weakness of laboratory experiments is that lab experiments can be low in ecological validity which means that results cannot always be generalised to everyday behaviours (Low external validity). This is particularly true if a study has low mundane realism.
• A strength of field experiments is that it has good internal reliability: Consistency within the procedures. Standardised procedures can allow for replication, however there is less control of the environment.

  Insight into everyday behaviour in real life settings. Field experiments are high in ecological validity
• A strength of field experiments is that the results are less likely to be affected by demand characteristics as participants often do not know that they are taking part in research.

  A cause and effect relationship can be established – The IV had a direct effect on the DV, however this can be affected by the lack of control on situational variables.
• 2 strengths of a Quasi experiment is that:

  •Insight into naturally occurring phenomenon that would be unethical to manipulate and therefore high in realism and ecological validity. •Attempts to establish a cause-and-effect relationship.
• 2 weaknesses of the quasi experiment is that: •Although a cause and effect relationship can be established the results may be low in internal validity as there is limited control of confounding variables such as the environmental and participant variables. •Participants are not randomly allocated into groups and therefore, a quasi experiment is not a true experiment.