Chapter 12: Experiments with More Than One IV

interaction/ interaction effects

the effect that one IV has on the DV depends on the level of another IV; a difference in differences/ difference in slopes

factorial design

experiments with 2 or more IVs

IVs are factors

participant variable

a variable that is selected, rather than manipulated, but treated as an IV in a factorial design, e.g. age

cells

unique combinations of treatment conditions

main effect/overall effect

overall effect of 1 IV on the DV, ignoring effects of other IVs (1 main effect per IV)

marginal mean

mean for each level of an IV when averaging over levels of the other IVs

how to determine if there is a main effect?

look at the marginal means for the 2 different levels within that specific IV and seeing if there is a difference between the 2

2x2 factorial design

2 IVs with 2 levels each

independent-groups/between-subjects factorial design

both IVs are manipulated as independent groups; each level of the IV becomes its own group

within-groups/repeated measures factorial design

both IVs are manipulated as within groups; if have x participants, going through all levels of the IVs, then we have 1 group with x participants

mixed factorial design

1 IV is treated as independent-groups, the other is treated as within-groups

how are factorials notated?

_ x _

no. of blanks tells you how many IVs there are (2 in this e.g.)

no.s that fill the blanks tells us how many levels each of the IVs have (2 levels for each IV)

two-way interaction

a difference in differences/slopes

three-way interaction

two-way interactions are different