Experimental Design

There are three main experimental designs, each with their own strengths and weaknesses.


  1. Separate groups of people are used in separate conditions.
  2. Strengths
    • Order effects (when participants become aware of or bored with an experimental procedure) are avoided.
  3. Weaknesses
    • Individual differences between groups, otherwise called “participant variables”, may affect the results (what if one group has people who have a naturally higher IQ than people in the other group?) – this lowers the validity of the experiment.
    • A larger amount of participants are needed in this experimental design.

independent measures


  1. Same group of people is used in different conditions.
  2. Strengths
    • Participant variable problems are avoided.
    • This experimental design requires less participants because the same group is re-used.
  3. Weaknesses
    • Order effects are very likely to occur; participants may become bored, aware or tired.

repeated measures


  1. Testing separate groups of people but each group’s members have their own common characteristics (e.g. same sex, same eye colour, same ethnicity, etc.).
  2. Strengths
    • The issue of participant variables is greatly reduced.
    • Order effects are totally avoided.
  3. Weaknesses
    • It is pretty much impossible to match people exactly on every characteristic; unless maybe they are identical twins – and even then, it is usually just matching physical characteristics.
    • It is very time-consuming to find lots of people that match each other so closely.

matched pairs

Solutions to reduce/eliminate order effects:
Counterbalancing means to change and alternate the order in which participants are performing different conditions during an experiment. For example: Group 1 does Activity A then Activity B and then Group 2 does Activity B and then Activity A.

Randomisation means to present material in random orders during an experiment.



17 thoughts on “Experimental Design

  1. Hello Maryam, I just wanted to send you some love and thank you for this brilliant website! It has provided me with all the help I needed.

  2. hi maryam you ve been an amazing help to me but i am a bit confused on how to attempt paper 2 its usually on themes and perspectives which you havent really given
    pls reply as soon as u can 🙂

      • Issues and debates:
        • the application of psychology to everyday life (its usefulness)
        • ecological validity
        • ethics
        • ethnocentric bias
        • reliability and validity
        • individual and situational explanations
        • nature and nurture
        • psychometrics
        • quantitative and qualitative data
        • generalisations
        • snapshot and longitudinal data
        • the use of children in psychological research
        • the use of animals in psychological research
        • reductionism
        • determinism.

        • the behaviourist perspective
        • the psychoanalytic perspective

  3. Hey, Maryam!
    All your work is extremely helpful and I really appreciate your efforts. I was wondering if you can also provide some detailed notes for AS Sociology?

    • Hi!

      Thank you, that’s really kind of you. I actually took A-Level Sociology as well and considered making a similar website for Sociology or Biology students when I started BlogPsychology… I just never got around to it because Psychology has always been my first choice.

      I’ll definitely consider it (after checking out the updated syllabus) and will let you know if I do start a similar website for students!

      Thanks for the feedback!

      Maryam XXX

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