Factorial designs

Question 1

Factorial designs:

Answer 1

Independent groups, Repeated
measures, or Mixed factorial designs

one consideration is total # of participants (costs)

Question 2

Mixed factorial design:

Answer 2

One IV is independent groups,
the other is repeated measures

Question 3

Use repeated measures rather than independent
groups whenever possible because….

Answer 3

• greater statistical power
• fewer subjects needed

Question 4

Independent factorial design:

Answer 4

Different groups of people in each condition.
(Example: Group 1 gets Drug A, Group 2 gets Drug B, Group 3 gets Drug A + B, Group 4 gets nothing.)
✅ No overlap — each person is only in one group.

Question 5

Repeated measures factorial design:

Answer 5

Same people go through all the conditions.
(Example: Everyone tries Drug A, then Drug B, then both.)
✅ Each person is their own comparison.

Question 6

Mixed factorial design:

Answer 6

Combination:

One factor uses different groups (between-subjects)

One factor uses the same people (within-subjects).
(Example:

Between: Group 1 vs Group 2 (different drug doses)

Within: Each group is tested both before and after treatment.)

✅ Good for studying both group differences and changes over time.

Question 7

Higher-order designs:

Answer 7

More than two IVs

Possible main effect of each IV and possible interaction for each combination of IVs.
- gender x major (Psy or Eng) x year in school = 2 x 2 x 4

• 3 possible main effects: gender, major, year in school
• 4 possible Interactions:

gender x major

gender x year in school

major x year in school

gender x major x year in school

Question 8

When you have two independent variables
(IV A and IV B):

Answer 8

• perform a two-way ANOVA
• evaluate main effect of A
• evaluate main effect of B
• evaluate interaction

The two-way ANOVA gives you three F-values (and
three corresponding p-values).

If p < α (usually .05), the main effect or interaction
being evaluated is significant

Question 9

When you have three independent variables
(IV A, IV B, and IV C):

Answer 9

• perform a three-way ANOVA
• evaluate main effect of A
• evaluate main effect of B
• evaluate main effect of C
• evaluate interactions between all combinations of two or more IVs:
  A x B
  A x C
  B x C
  A x B x C

The three-way ANOVA gives you 7 F-values (and 7 p-values)