Experimental design

• Laboratory experiment = a controlled environment where extraneous and cofounding variables (EVs and CVs) Can be regulated. Partcipants go to researcher. The IV is manipulated and the effect on the DV is recorded.
• Laboratory experiment advantages = + EV’s and CV’s can be controlled. This means that the effect of EV’s and CV’s on the DV can be minimised. Cause and effect between the IV and DV can be demonstrated (high internal validity).

  + Can be more easily replicated. greater control means less chance that new EV’s introduced. This means that findings can be conformed, supporting their validity.
• Laboratory experiment disadvantages = - 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).

  - demand characteristics may be a problem. these are cues in the experimental situation that invite a particular response from participants. The findings may be explained by these cues rather than the effect of the IV (lower internal validity).
• Field experiment = a natural setting. The researcher goes to participants. The IV is manipulated and the effect on the DV is recorded.
• Field experiment advantages = + more natural experiment. Participants more comfortable and behaviour more authentic. Results may be more generalisable to everyday life.

  + 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.
• Field experiment disadvantages = - more difficult to control CV’s/EV’s. Observed changes in the DV may not be due to the IV, but to CV’s/EV’s instead. It is more difficult to establish cause and affect than in the lab .

  - there are ethical issues. Participants in afield experiment may not have given informed consent. This is an invasion of participants privacy, which raises ethical issues.
• Natural experiment = the experimenter doesn’t manipulate the IV( it does change, but the change is not made by the experimenter) someone or something else causes the IV to vary. The IV would have varied even if the experimenter wasn’t interested. DV may be naturally occurring (e.g. exam results) or may be devised by the experimenter and measured in the field or a lab.