design

• what are independent groups

  this is where the Ps only do one of the experimental conditions
• what are matched pairs

  this is where the Ps only do one of the experimental conditions, but the Ps are matched into pairs based on important characteristics- usually an extraneous variable

  one person from the pair is randomly allocated to one experimental condition and the other person does the other experimental condition
• what are repeated measures

  this is where the Ps do all of the experimental conditions
• what are order effects

  these are a consequence of Ps doing all of the conditions : the order in which they do the conditions in may affect their performance in the second condition instead of the manipulation of the IV
• what are practise effects

  Ps may become practised at the test and so their performance will improve
• what are fatigue effects

  Ps may become tired of the test and so their performance will deteriorate
• what is a strength of independent groups

  no order effects- as the Ps will only take part in the experiment once so they will not display practise effects or fatigue effects - this increases the internal validity as the researcher can be sure that the manipulation of the IV is causing the change in the DV and not anything else
• what is another strength of independent groups

  fewer demand characteristics- Ps only take part in experiment once and they are less likely to guess the true aim of the study- this increases the internal validity as fewer demand characteristics mean fewer confounding variables
• what is a weakness of independent groups

  with this design, twice the amount of Ps are needed- this means it takes longer to carry out and is more costly- therefore it is not a practical participant design
• what is another weakness of independent groups

  participant extraneous variables- as there are different Ps in each condition there could be individual differences- the findings could be due to participant variables and not the manipulation of the Iv- this makes it harder to establish cause and effect between the IV and Dv which reduces the internal validity
• what is a strength of matched pairs

  no order effects and fewer demand characteristics
• what is another strength of matched pairs

  an attempt has been made to control extraneous variables - each experimental condition has similar types of people in it - this means that participant extraneous variables has been reduced which increases the internal validity
• what is a weakness of matched pairs

  less economical and participant extraneous variables
• what is another weakness of matched pairs

  less economical- it takes time and effort to screen people for extraneous variables and match them into pairs- practically matched pairs is not a good design
• what is a strength of repeated measures

  participant extraneous variables are controlled so there will be no individual differences- therefore the experimenter can be sure that the manipulation of the IV is causing the change in the DV- this increases the internal validity as there are fewer extraneous variables
• what is another strength of repeated measures

  more economical- half the number of Ps are needed-this means the experiment can be conducted more quickly and it will cost less to complete- this makes it a practical participant design
• what is a weakness of repeated measures

  Ps take part in both conditions- this means their performance in the second condition may not be due to the manipulation of the IV but due to the fact that it is the second time they are doing the task- the reduces the internal validity
• what is another weakness of repeated measures

  demand characteristics- Ps complete all of the conditions so the Ps may guess the true aim of the study and change their behaviour accordingly- they may try to please the experimenter or try to sabotage the study- this reduces the internal validity due to extraneous variables