experimental methodlogy

• Lab experiments features:

  • controls variables and environment
  • low external validity
  • reliable
  • participants likely to be deceived
  • experimenter effects
• Field experiments features:

  • high ecological validity
  • cannot replicate
  • better ethics
• what is an independent variable?

  The variable being manipulated by researcher
• what is the dependent variable ?

  One this is measured the effect of IV on
• what is independent groups design ?

  Different participants are allocated to two or more experimental groups representing different levels of the independent variable

  may be a control group
• what is repeated measures design?

  Each participant takes part in every condition being tested
• what is matched pairs design?

  Participants who are very similar on key variables are paired, one member of the pair is placed in group A and other in group B
• what is counterbalancing ?

  when participants from practice have experience from previous condition resulting in the effect being cancelled out
• Repeated measures

  +good control of participant variables as same person is being tested twice or more

  -order effects are produced and participants may guess the purpose of the experiment due to doing both conditions
• Independent groups

  +avoids order effects

  -no control over participants variables
• matched pairs

  +control avoids order effects

  -very time consuming to match participants on key variables
• Participant variables

  • age
  • intelligence
  • personality
• situational varibales

  • location
  • temp
  • time of day
• What is the importance of operationalisation?


  To avoid extraneous variables we must ensure we operationalise out IV and DV correctly- by making sure we are measuring what we intending to measure
• what is reliability?

  for something to be able to be replicated and resarchers get the same or similar results- consistency
• how can we improve reliability?

  Take more than one measurement from a participant

  Pilot studies can be used to check that the proposed method of measurement is suitable. To improve inter-rater reliability then ensure all researchers process of collecting data is standardised
• what is internal validity?

  The ability of the study to test the hypothesis that it was designed to set, measuring the effects of the IV on the DV
• how can we improve internal validity?

  Single blind technique where participants don't know the condition they have been assigned to

  Double blind technique removes demand characteristics and experimenter bias
• what is external validity?

  how well the results can be generalised beyond the study itself

  • ecological validity- generalising results to real life setting