PSYCH IB-experimental design

• counterbalancing


  an experimental technique used to overcome order effects when using a repeated measures design. counterbalancing ensures that each condition is tested first or second in equal amounts
• experimental design 


  a set of procedures used to control the influence of factors such as participant variables in an experiment
• independent groups design


  participants are allocated to two or more groups representing different levels of the IV. allocation is usually done using random techniques
• matched pairs design


  pairs of participants are matched in terms of key variables such as age and IQ. one member of each pair is allocated to one of the conditions under test and the second person is allocated to the other condition
• order effect


  in a repeated measures design, an extraneous variable arising from the order in which conditions are presented, e.g. a practice effect or fatigue effect.
• random allocation 


  allocating participants to experimental groups or conditions using random techniques
• repeated measures design


  each participant takes part in ever condition under test, i.e. each level of the IV
• experimental design


  a comparison condition where there are different levels of the IV needs to be present to find out whether the IV effects the DV
• repeated measures-advantages


  1.the order of the conditions may affect performance(an order effect). may do better on second test because of a practice effect or because they are less anxious. may do worse on the second test due to boredom effect.

  2. when participants do the second test they may guess the purpose of the experiment, which may affect their behaviour.
• repeated measures-dealing with disadvantages 


  researchers may use two different tests to reduce a practice effect-though they must be equivalent. the main way that order effects are felt with is the use of counterbalancing. a cover story can be presented to avoid participants guessing the aims of the study
• independent groups-disadvantages

  1. the researcher cannot control the effects of participant variables. for example group A may have better memories than group B. this would act as a confounding variable.
  2. independent groups design needs more participants than repeated measures design in order to end up with the same amount of data
• independent groups- dealing with disadvantages


  randomly allocate participants to conditions which (theoretically) distribute participant variables evenly. random allocation can be done by putting the participants’ names in a hat and drawing out the names so that every other person goes in group A
• matched pairs-disadvantages 


  1.it is very time consuming and difficult to match participants on key variables. the researcher probably has to start with a large group of participants to ensure they can obtain matched pairs on key variables.

  2. it is not possible to control all participant variables because you can only match on variables know. to be relevant, but others may be important.
• matched pairs- dealing with disadvantages

  restrict the number of variables to match on to make it easier. conduct a pilot study to consider key variables that might be important when matching