Two-Way Experiments Flashcards
When is a two way experiment used
When a researcher wants to study how a DV is affected by 2 different IVS
Why is it better to do a two way experiment rather than 2 separate experiments?
More efficient
You can test the COMBINED effects of the 2 IVS
how many conditions would a 2x2 have?
4
How many conditions would a 3x3 have?
9
When you have 2 IVS, you describe the design with…….
2 numbers that indicate how many levels of each IV
e.g., 2x2, 2x4, 3x3 etc.
When you have 3 IVS, you have ___ numbers
3 numbers
e.g., 2x2x2, 2x3x4
we might find that the IV’s ________ or _________
combine additively (joint effects on DV)
A&B = A + B
OR
interact
the effect of A depends on the presence or absence of B and vice versa
the combined effects of A&B (interaction) might be _______
greater than or less than the variables independent effects
Overall main effect of an IV
averaging its effects across all levels of the other IV
simple main effect of an IV
find the effect of one IV at a specific level of the other IV ( e.g., a treatment on its own: JUST treatment A & not treatment A&B)
example of an additive effect:
No Drug B, No Drug A: 100
No Drug B, Drug A: 110 : (+10)
Drug B, No Drug A: 120 : (+20)
Drug B, Drug A: 130 : (10+20)
ADDITIVE
example of an interaction effect:
No Drug B, No Drug A: 100
No Drug B, Drug A: 100
Drug B, No Drug A: 100
Drug B, Drug A: 125
INTERACTION produced an effect
Another example of an interaction effect:
No Drug B, No Drug A: 100
No Drug B, Drug A: 110
Drug B, No Drug A: 110
Drug B, Drug A: 110
INTERACTION
BUT
smaller than what an additive effect would be (additive would be 120)
In this case Drug A only works for improving memory when drug B is absent, and vice versa
To test for main effects compare results across all levels:
compare calculated mean groups with one IV (if 2x2 you will have 5 calculated means)
(ex. Drug A - No Drug A)
the difference in size is the main effect
