experimental designs

• experimental design? 


  the different ways in which participants can be organised in relation to the experimental conditions
• independent groups design? 


  participants allocated to different groups where each group represents one experimental condition
• repeated measures? 


  all participants take part in all conditions of the experiment.
• matched pairs design? 


  pairs of participants are first matched on some variable that may affect the dependent variable. then one member of the pair is assigned to condition A and other pair to condition B.
• random allocation? 


  an attempt to control for participant variables in an independent groups design which ensures that each participant has the same chance of being in one condition as any other.
• counterbalancing? 


  an attempt to control for the effects of order in a repeated measures design: half the participants experience the conditions in one order and the other half in the opposite order.
• strengths of independent groups design?

  order effects aren't a problem whereas they are a problem for repeated measures designs. participants are also less likely to guess the aims.
• limitations of independent groups design?

  participants who occupy the different groups aren't the same in terms of participant variables. if researcher finds a mean difference between groups on the DV may be more to do with participant variables not IV. differences act as confounding variables reducing the validity of the findings.

  less economical than repeated measures as each participants contributes a single result only. twice as many participants needed to produce equivalent data to that collected in repeated measures design so increases time/money spent on recruiting participants.
• limitations of repeated measures?

  order effects present as order of the tasks done may be significant. use counterbalancing to deal with this

  repeating two tasks can create boredom or fatigue that cause deterioration in performance on 2nd task so matters what order the tasks are in.

  demand characteristics are a feature as participants could work out the aim when they experience all conditions
• strength of repeated measures?

  participant variables are controlled so higher validity.

  fewer participants needed so less time spent recruiting them.
• strength of matched pairs design?

  order effects and demand characteristics less of a problem as participants take part in one condition.
• limitation of matched pairs design?

  matching may be time consuming and expensive so less economical than other designs.

  attempts to reduce participant variables however participants can never be matched exactly even when identical twins are used there's still important differences between them that affect the DV.