• Only true experiments allow researchers to make a causal conclusion based on study results.
  
  
• True experiments require that the independent variable is under direct control of the experimenter and that researchers attempt to control extraneous factors that might influence study results.
  
  
• Random assignment is used in between-subjects designs to control extraneous factors.
  
  
• Randomization and counterbalancing are used in repeated-measures designs to control extraneous factors.

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