Wk4: Interactions

Question 1

Main effects have a _________ effect on the DV

Answer 1

Additive

Question 2

Define order of interaction

Answer 2

Number of IVs (not levels)
e.g. IV1 = 4 levels, IV2 = 5 levels, IV3 = 2 levels;
3 orders total

Question 3

Combination formula

Answer 3

nCr = n!/ (r! (n-r)!)

Question 4

Name the interactions of a 2x2x2 design

Answer 4

• 3 main effects (A, B, C)
• 3 two-way interactions (AB, BC, AC)
• 1 three-way interaction (ABC)

Question 5

Name the interactions of a 4-way design

Answer 5

• 4 main effects (A, B, C, D)
• 6 two-way interactions (AB, AC, AD, BC, BD, CD)
• 4 three-way interactions (ABC, ABD, ACD, BCD)
• 1 four-way interaction (ABCD)

Question 6

Disordinal interactions must have:

Answer 6

1. Slopes have different direction
2. Intersection of lines

Question 7

What’s stronger: ordinal or disordinal?

Answer 7

Disordinal interactions are stronger.

Question 8

Problems with ordinal interactions

Answer 8

• Scaling artifacts
• MSMT artifacts: floor ceiling effects
• MSMT artifacts: regression to the mean

Question 9

What are scaling artifacts?

Answer 9

• The scale used may not accurately reflect real-world differences.
• Present in ordinal-scales and below (interval and ratio do not have scaling artifacts)
• E.g. in a 0-10 attractiveness scale, the difference between 4-5 is less than 8-9.

Question 10

What are floor/ ceiling effects?

Answer 10

• The measurement used may have results that “pool” near the top/ bottom of the scale, meaning results cannot increase/ decrease a significant amount.
• E.g. In a reading test, comparing 1st and 4th quartile students after a program, the 1st quartile improved much more than the 4th, but only because the 4th could not test higher than 100% on tests.

Question 11

What is regression to the mean?

Answer 11

• The tendency for scores to become more average over time
• E.g. Those who score high on a true/false quiz without studying will likely score closer to 50% on the next try because they were always likely to score 50%, it was just chance the first time.