within subjects

-typical experimental procedure

-each group contains different people

-comparisons are between different groups

-independent variable represents more than one assessment of the same group, under different conditions

-other IVs may be between subjects (mixed design)

-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

• -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

-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

• -internal validity
• *eliminate confound of group differences at baseline
• *lessens carry-over effects

-statistical power design requires more subjects

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

• -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

• -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.

-carryover effects

-maturation

-testing

-own control design create stonrg contrast for IV

-eliminate probems in creating experimental versus control group