features of experimental design

• order effects - this occurs when participating in one condition may affect how a participant performs in another.


  practice effect - participants may perform better in the experiment condition but because of practice after completing the control condition.

  fatigue effect - participants may perform worse in the experiment condition, not because of the IV being manipulated, but because of boredom or fatigue
• counterbalancing is used to reduce or eliminate order effects by ensuring that all possible orders are represented equally
• demand characteristics - a type of confounding variable where participants unconsciously work out the aim and act differently, either:


  social desirability - some participants may purposely change their behaviour in order to present themselves in a positive light.

  "screw you" effect - participants work out the aim of the experiment, and deliberately act differently to destroy the experiment.
• the number of participants required to collect a sufficient amount of data depends on which experimental design you use.

  • using fewer participants is a pratical choice in research and can save a great deal of time and effort.
• participant variables


  some participants may have specific characteristics that will enhance their ability, giving them an unfair advantage in comparison to other participants.