experimental design

• repeated measures design

  only one group of participants is used. This group does both conditions of the experiment.
• Independent group design

  A separate group of participants used for each condition of the experiment
• strengths of repeated measures

  Individual differences are removed

  you need less participants

  can get more data
• Limitations

  order effects- the order of the condition could effects performance for example their performance in a second condition may be helped through practice of a task they did first.

  demand characteristics - participants guess the aim of the study and alter their behaviour by having a "please you effect" or a "screw you effect".
• RM: dealing with the limitations 


  use two different tests to reduce a practice effect. However the two tests must be equivelent in terms of difficulty

  researcher come up with a fake aim to cover up the true aim (single blind study)

  counterbalancing
• Independent group design strengths

  no order effects
• independent group design: limitations

  no control of participant variables. For example participants in group one may be more able than participants in group two

  you need twice as many participants
• IGD: dealing with limitations

  randomly allocate participants to conditions to ensure that the groups are equal
• matched pairs design

  controls some participants variables

  participants wont guess the aim

  no order effects
• matched pairs design: limitations

  achieving matched pairs is difficult and time consuming

  may be to costly to undertake

  may not control all participants variables
• MPD: dealing with the limitations

  restrict the number of variables to be matched on

  A plot study could show key variables that need to be matched
• counterbalancing

  equal number of participants undertake the task required of them in different orders. For example group 1 does condition 1 whilst group 2 does condition 2. Then they switch
• randomisation

  deciding the order of presentation of experimental conditions. For example tossing a coin.
• pilot studies

  A small scaled investigation that takes place before the actual research is conducted.

  The aim is to check the method.eg the procedures, materials, measuring scales etc all work properly.

  Allows researchers to make changes and modifications if necessary.

  They are used in experimental and non experimental methods