within subjects

  1. overview of between (independent) subjects designs (3)
    -typical experimental procedure

    -each group contains different people

    -comparisons are between different groups
  2. overview of within subjects designs (2)
    -independent variable represents more than one assessment of the same group, under different conditions

    -other IVs may be between subjects (mixed design)
  3. COre issues of within subjects designs (3)
    -many research questions address contrasts between different states within one person.

    -many studies address change over time

    • -practical efficiency of within Ss designs
    • *powerful contrasts within subjects; less within group variance
    • *studies that require rare or costly participants
  4. Basic between-subjects design (4)
    • -clear experimental manipulation
    • *treatment given to only one group

    -hypothesis tested via differences between groups

    -internal validity groups must differ only on IV

    statistical power
     requires larger number of subjects
  5. Within subjects designs
    -hypothesis tested by differences between conditions within group

    -internal validity: eliminate possible confound of group differences at baseline since there is only one group

    -statistical power increased, requires fewer subjects

    -experimental manipulation potentially less clear

    • -possible carry-over effects
    • ***efefcts of being in one experiment then going into anohter but carrying those effect over
  6. Within subjects designs with Counter balancing?
    • -internal validity
    • *eliminate confound of group differences at baseline
    • *lessens carry-over effects

    -statistical power design requires more subjects
  7. whats counter balancing?
    one group will be set for control while the other is experimental in the within subjects design to prevent carry-over effects. then they switch
  8. Advantages of within subjects designs (3)
    • -participant assignment problems eliminated, since there is only one group
    • *no need for random assingment
    • *no problem wiht groups being equal at baseline

    • -can use a smaller n than between Subjects
    • *half as many participants
    • ** very useful for rare or expensive participants

    -more senstive to experimental effects; less within subject (error) variance
  9. Disadvantages of within-subjects designs
    • -participant "burden"
    • *fatigue from multiple experimetns
    • *possibly drop out

    • -sequencing or order effects
    • *scores change if participants learn or get practice over different conditions
    • *participants get sensitized to experiment
    • *cure by counter-balncing order of condition takes about as many participants as between group design.
  10. Brief problems on within subjects designs
    -carryover effects


  11. Within subjects design are somewhat common in psychological research
    -own control design create stonrg contrast for IV

    -eliminate probems in creating experimental versus control group
Card Set
within subjects