Experimental designs

• Independent measures

  • different participant are used in each condition
  • Done randomly to ensure that each participant has equal chance of being assigned to each group
• Repeated measures 

  • same participants takes pry in both conditions 
  • Means each condition of experiment includes same group of participants 
• Matched pairs

  • pairs of participants are matched in terms of key variables such as age
  • one member of each pair is placed in the two different conditions 
• Hypothesis 

  Null 

  • any effect is due to change, there is no relationship/ difference 
• Alternative hypothesis

  • states there will be a difference due to manipulation of IV
  • Can be referred to as an experimental hypothesis 
  • Can be one tailed/ directional or two tailed/non directional 
• one tailed


  directional e.g there will be a specific difference
• two tailed


  non-directional e.g there will be a differnce
• Field experiment 


  conducted in a natural environment
• Laboratory experiment


  done in a controlled environment
• field experiment strengths

  • natural environment
  • High ecological validity 
  • Easier to observe Natural behaviour 
• field experiment weakness


  • lacks control of extraneous variables
  • Might effect the results to to lack of internal validity
• Laboratory experiments strengths


  • Controlled environment
  • Controls for extraneous variables ensure external variable don’t effect results
• laboratory experiment weakness 


  • artificial setting
  • might effect behaviour of participants due to the unnatural environment
  • behaviour observed may not be natural study lacks ecological validity
• Demand characteristics:

  are cues in a research situation that communicate to participants what is expected of them and may then unconsciously affect behaviour of participants 
• Single blind-technique:

  The participants are not aware of what is expected or the condition they are in. But the person carrying out the study is aware.
• Double blind-technique:

  Neither the participant nor the person running the study knows what is expected. The participants are not aware which group they are in or what the study is about. The study is carried out by someone other than the experimenter. 
• What are participant effects?

  • The fact that participants react to cues in an experimental situation. These include responding to demand characteristics - Features of an experiment that a participant unconsciously responds to when searching for cues about how to behave. They may alter their behaviour by trying to please the experimenter or behave in a way that is unexpected.