experiments and variables

• three types of experiments

  • laboratory
  • field experiments
  • quasi experiments
• confounding variable

  a variable that affects the dependent variable
• extraneous variable

  a variable that could affect the dependent variable but has been controlled for so it doesn't
• participant variables

  individual differences
• situational variables


  any feature of the experiment that could influence a participants' behaviour e.g. weather
• laboratory experiments


  a study in a contrived environment, ppts come into this setting to be part of the study but would not be there normally

  many variables can be controlled that may influence the participants' behaviour, e.g. standardising instructions
• field experiments


  study in participants' normal environment - in relation to the behaviour being investigated

  participants should be relatively unaffected by being in the experiment - not know they are
• quasi (natural) experiment


  no control over the independent variable - it's naturally occurring e.g. gender

  makes use of natural changes or differences in circumstances to provide the experimental conditions

  can be conducted in lab/field settings - used when it is impractical or unethical to generate the conditions necessary for different levels of the IV
• strengths of lab experiments

  • good control of extraneous variables
  • casual relationships can be determined
  • can be replicated (due to strict procedures) so researchers can be more confident in their findings
• weaknesses of lab experiments

  • artificial situation could make participants' behaviour unrepresentative
  • participants could respond to demand characteristics and alter their behaviour
• strengths of field experiments

  • participants' behaviour likely to be representative as they are in their normal situation
  • demand characteristics less likely than in lab experiments as participants are often unaware they are in a study
• weaknesses of field experiments

  • less reliable and replication is more difficult due to less control over extraneous variables
  • researcher cannot be sure that changes in the DV have been caused by changes in the IV
  • ethical issues raised as participants are unaware they are in an experiment
• strengths of quasi experiments

  • can be used to study real-world issues
  • behaviour is likely to be representative if participants' are in their normal situation
  • demand characters are less problematic if participants' are unaware that they are in a study
  • enables researchers to investigate variables that could not practically or ethically be manipulated
• weaknesses of quasi experiments

  • only possible when naturally occurring differences arise
  • control over extraneous variables is often very difficult
  • researchers are less sure of the cause of changes in the DV i.e. a casual relationship cannot be established
  • hard to replicate
• reliability in experiments

  • laboratory experiments - researcher can impose controls such as standardised procedures -> increase reliability as ensures all participants are treated in the same way
  • field experiments (and some quasi experiments) - variables harder to control when in participants' normal environment -> likely greater variation between the precise circumstances under which the DV is measured between participants, lowering reliability
  • controls that make replication easier can increase reliability as findings are reliable - hard to achieve in quasi experiments
• validity in laboratory experiments

  • laboratory experiments - extraneous variables are controlled, researcher can make sure changes in the DV have been caused by the IV -> validity is high
  • laboratory experiments - measure of the DV tends to be quite artificial -> participants' responses are being measured in a way that doesn't reflect day-to-day life, decreases validity