Lecture 3

Question 1

Why is theory of error important?

Answer 1

• need a theory of error to find the truth
• OR to determine if the observation supports our theory
• statistical provides a theory of error

Question 2

What is GLM? What is important about this?

Answer 2

adding up variables using a weighted sum - there is no variation though!
So add the error term to allow for variation > can then use the same equation for everyone, just change the error term and you can always get it to fit

Question 3

What is a theory of error?

Answer 3

• error term that requires statistical techniques
• eg. residuals (estimates of error), normal distribution
• usually assume that the error is normally distributed

Question 4

What are the assumptions of regression?

Answer 4

• residuals are normal
• mean of 0 for residuals
• independent residuals
• homoscedasticity
• look at P-P plot, histogram and scatterplot

Question 5

What is mediation? What is the simplest mediation model?

Answer 5

• one variable acts on another through an intervening (mediating) variable
• simplest: X > M > Y

Question 6

What do a, b and c’ represent in mediation?

Answer 6

• a = effect of X on M
• b = effect of M on Y
• c’ = effect of X on Y (if it is 0, then there is complete mediation)

Question 7

What are the indirect, direct and total effects in mediation?

Answer 7

• a*b = indirect effect
• c’ = direct effect
• a*b + c’ = total effect
• c = total effect too (c = c’ + a*b)

Question 8

What is the Sobel test?

Answer 8

• null = indirect effect is 0 (a*b=0)

- if p less than 0.05, then indirect effect is sig.

Question 9

What are the issues with the Sobel test?

Answer 9

• not always effective
• bc. of low power
• bc. of non-normality in distribution of mediated effects

Question 10

What is a bootstrap CI? Why is it good?

Answer 10

• bootstrap takes many samples of your sample to get a sampling distribution
• without any assumptions of normality
• is CI includes 0 = significant indirect effect (sig. mediation)

Question 11

How to you tell if partial or complete mediation from the PROCESS output?

Answer 11

• if direct effect not sig., but indirect sig. then there is complete mediation
• if direct effect sig. and indirect sig., then partial mediation

Question 12

What do you look at in the PROCESS script output for mediation?

Answer 12

• look at X, Y and M to see which variables are being used
• check sig. of predicting the diff variables
• sig. of direct effect
• look at indirect effect CI (don’t want to include 0)
• look at ‘normal theory tests’ = Sobel test. Want p less than .05

Question 13

What are the 4 requirements for mediation?

Answer 13

• IV directly predicts DV (c significant)
• IV directly predicts MV (a significant)
• MV directly predicts DV (b significant)
• crucial step: IV and MV both predict DV (IV either eliminated or partially reduced)&raquo_space;> same as saying c’ is sig. smaller than c (reduction) OR c’ is not sig./0 (elimination)

Question 14

What is the mediation regression equation?

Answer 14

Y = b3 + c’X + bM + e3

Question 15

What is moderation?

Answer 15

• 1 variable moderates the association b/w 2 variables when the association differs depending on the value of the moderating variable
• INTERACTION b/w M and X

Question 16

What is the moderation regression equation? How can it be rearranged?

Answer 16

Y = b0 + b1X + b2M + b3XM + e

Y = (b0 + b2M) + (b1 + b3M)X + e

• if b3 is sig > there is moderation occurring

Question 17

What depends on M? Which terms represent this?

Answer 17

BOTH slope and intercept

• mediated intercept: b0 + b2M
• mediated slope: b1 + b3M

Question 18

What do you look at in the PROCESS output for moderation?

Answer 18

• interaction p value (want less than 0.05 for sig.)
• diff ‘effects’ (slopes) for diff values of moderator > how the slope changes, can change direction and strength
• look at where the sig. moderation stops being sig.
• look at “Johnson and Newman” output to determine where the moderator stops being sig. (look at p values and CI)

Question 19

How do you graph moderation?

Answer 19

• save PROCESS output called “data for visualizing conditional effect of X on Y”
• make scatterplot of yhat vs. IV (set markers by M)
• look at slopes/intercepts and how they differ for diff values of M
• can also plot effect, LLCI and ULCI to see where the association stops being sig.
• where it includes 0, the moderator is so strong that association b/w Y and X is no longer significant

Question 20

How can you tell how many dimensions a line is in?

Answer 20

• how many things there are in the equation (not error though)
• # IVs + constant(1)

Question 21

What are the 3 mediation equations according to Baron and Kenney?

Answer 21

Y = B + cX + e
M = B + aX + e
Y = B + c'X + bM + e

Question 22

Why do only test whether the indirect effect is sig. in mediation?

Answer 22

Because ab = c - c’

This is the critical criteria

Question 23

What do you do Sobel and bootstrap do not agree?

Answer 23

Use bootstrap, it is better

Question 24

What happens is error is random?

Answer 24

• it should cancel out across all subjects in the sample

- this is good!

Question 25

What does modern mediation say?

Answer 25

• a*b sig.
• c also sig.
• just test a*b

Question 26

What is moderation based on? What way can you do this other than PROCESS?

Answer 26

• all about simple slope and the standard error of it
• can test with t-test of (b1 + b3M)/SE(slope)
• df: N - k - 1 (N = sample size, k = no. predictors in interaction term)