types of experiment

• lab experiment

  Laboratory experiments are conducted under controlled conditions, in which the researcher manipulates the independent variable (IV) to measure the effect on the dependent variable (DV).
• how are environmental factors controlled in lab experiments

  using standardised procedures
• IV and DV in a lab experiment

  The IV is changed by the researcher between the conditions of the experiment. Any change in the DV will be measured while all other variables that could change the DV are kept consistent between conditions
• lab experiment strengths

  • by controlling all variables that may affect the DV, a cause and effect relationship can be established between the changes in the IV and the observed difference in the DV
  • High internal validity meaning observed change in DV is due to change in IV
  • Have high reliability and replicability due to the use of standardised procedures
• lab studies weaknesses

  • can lack ecological validity, a type of external validity. This means findings from a lab study can’t be generalised to real life settings
  • tasks studied in lab studies lack mundane realism(task isn’t realistic) which lowers external validity
  • participants are aware they are in a study and may alter their behaviour due to demand characteristics to match the aim
• field experiments

  Field experiments are conducted in a natural setting (e.g. at a sports event or on public transport), as opposed to the artificial environment created in laboratory experiments.
• IV and DV in a field experiment

  IV is still manipulated by the researcher between the conditions of the experiments and the researcher then measures the difference in the DV
• field experiment strengths

  • participants are more likely to behave naturally in their normal environment, making it more likely any behaviour can be applied to other natural settings(ecological validity)
  • tasks are more likely to have mundane realism, so will be closer to the type of activities participants normally do
  • if participants are unaware they are in an experiment, they will not show demand characteristics
• field experiment weaknesses

  • field studies lack control over possible extraneous variables that could affect the DV
  • in many field studies, it is difficult to randomly assign participants to conditions, resulting in a change in the DV that may be due to participant variables, reducing internal validity
  • ethical issue- if participants do not know that they are being studied, is it right to manipulate and record their behaviour?
• natural experiments

  Natural experiments are carried out in natural conditions, however the researcher is unable to manipulate the IV and therefore examines the effect of a naturally occurring variable on the dependent variable (DV).
• IV and DV in a natural experiment

  The IV is not changed by the researcher between the conditions of the experiment. Changes in the DV are still measured but other possible variables that could change the DV cannot be controlled
• natural experiment strengths

  • allow research in areas that couldn't happen in controlled experiments due to ethical or cost reasons
  • high in external validity as natural experiments are an example of real behaviour occurring in the real world WITHOUT demand characteristics
• natural experiment weaknesses

  • as the events have already happened regardless of the researcher, they have no influence. This means that extraneous variables can't be controlled, so the researcher can't claim they have found a cause and effect relationship
  • these are often very rare events that cannot be replicated to test for reliability
• quasi experiments

  participants cannot be randomly assigned between levels of IV, often because the IV is an innate characteristic of the participants like eye colour
• IV and DV in quasi experiments

  IV already exists in the participants so participants can't be randomly allocated to the conditions of the experiment. The difference in the DV will be measured while all other possible variables that could change the DV are kept constant.
• quasi experiment strengths

  • quasi experiments are the only way to experimentally study factors that are pre-existing characteristics of participants
  • Less experimenter bias in participant condition allocation, as the researcher does not pick which condition to put participants in.
• quasi experiment weaknesses

  • there is a higher chance of extraneous variables, especially partcipant variables as partcipants are not randomly allocated to each condition
  • Participants may be aware of being studied, creating demand characteristics and reducing internal validity.