control of variables

• standardisation

  putting in place control to ensure every aspect of the research is the same for all participants and meets a consistent standard - includes standardised environment (laboratory), standardised procedures (same materials and timings), standardised instructions (scripting/pre-recording)
• randomisation


  ensuring all choices are randomly selected by chance (using random name generator) rather than being determined by the researcher - most common example, when using separate groups of participants in different conditions, ensuring random allocation of participants to conditions to avoid researcher bias
• confounding variables


  an extraneous variable that hasn't been controlled and may therefore have spoiled the results - no longer clear if any change in the DV was caused by the IV or the confounding variable - if a study has confounding variables, the results are invalid