Only $35.99/year

Research Methods & Stats III Midterm

Terms in this set (40)

After centering your moderator variable, it can be useful to understand the impact of the moderator at high and low levels of the variable - ONLY do if b3 is significant
Using the centered version of Stress (Stress_g) provides us with an interpretable estimate of the treatment effect (i.e., b1)
Coeff b1 is now specific to a person with 'average' Stress
However, recall that the significant b3 coefficient suggests that this treatment effect (i.e., b1) depends on a person's level of Stress!
We need a way to evaluate and illustrate how the tx effect (slope of b1) changes as a function of Stress
i.e., How does having a lower or higher level of stress depend on a stronger or weaker treatment effect?
-When stress is high, there's a positive effect of b1
-When stress is low, there's a negative effect of b1

Steps:
Manipulate the 0-point of the moderator
'Benchmark' values are ±1 SD
Consider using Q1 and Q3 if moderator is highly skewed and/or kurtotic
1. Create 'low' and 'high' versions of Stress to 'shift' 0-point:
LowX2 = X2_g + 1 SD
0 in LowX2 now represents someone who is 1 SD below the mean in X2
HighX2 = X2_g - 1 SD
0 in HighX2 now represents someone who is 1 SD above the mean in X2
2. Results in 2 simple regression equations for 'low' and 'high' levels of mod

Low (1 SD Below Mean) Mod Equation:
BAI=b0+b1*BPTdum
BAI=52.51+0.36*BPTdum

High (1 SD Above Mean) Mod Equation:
(BAI)=b0+b1*BPTdum
BAI=60.73+(-7.21)*BPTdum

In these above equations, the "low" slope is positive, and the "high" slope is negative (thus, b3 is likely to be negative)