Session 7: Introduction to R

Question 1

Before we begin to analyze our data…

Answer 1

• be sure that data does not include any info that might identify individual participants
• have a safe place (where you can store data)
• create backup files
• raw data -> correctly recorded?

Question 2

Preliminary analyses

Answer 2

• for multiple-response measures: assess the internal consistency
• analyze ech important variable seperately
  (distribution, central tendency, variability, outliers, etc.)

Question 3

Mediator

Answer 3

a mediating variable transmits the effect of an antecendent variable on t a dependent variable, thereby providing more detailed understanding of relations among variables

Question 4

Moderator

Answer 4

A moderator M is a variable which affects the strength or nature of the relationship between two other variables

Question 5

Regression equation for moderation of the linear relationship between X and Y

Answer 5

Y = b0 + b1X + b2M + b3XM

Question 6

Steps od the moderation analysis

Answer 6

1. Mean center independent variable X and moderator variable M
2. Multiple mean centered independent variable and mean centered moderator variable
3. Linear regression with main effect , then linear regression with main effects and intercation term
4. Visualization
5. Simple Slope Analysis (2 options)

Question 7

If the M variable takes on a value that is one standard deviation above it’s mean, then…

Answer 7

the M.c (mean centered moderator) variable takes on the positive standard deviation of the M variable

Question 8

If the M variable takes on a value that is one standard deviation below it’s mean, then…

Answer 8

the M.c (the mean cenetered moderator) takes on the nagtive standard deviation of the M variable

Question 9

What happen when you mean center the variables?

Answer 9

• mean of the mean centered variables is 0

- standard deviation stays the same!!

Question 10

Step 2 - Intercation term

Answer 10

multiply the two mean centered variables in order to create an interaction term :)

Question 11

Step 3 - regressions

Answer 11

a)Regression with main effects
b)Regression with main effects and the interaction term
(to enable easier interpretation - regression equation)

Question 12

Step 4 - Visualization

Answer 12

We can plot the moderation effect by calculating the predicted values of Y under different conditions (high and low value of X and high and low value of M)
- plot the predicted relationship between X and Y at different values of the moderator

Question 13

Step 5 - Simple Slope analysis

Answer 13

• we know that the lines differ significantly from each other
• we want to find out more about the relationship of X and Y at particular levels of the Moderator (M)
• for this purpose we assess simple slope tests

Question 14

What are simple slope tests?

Answer 14

are used to asess wthether the relationship (slope) between X and Y is signficant at a particular value of the moderator

Question 15

How do we perform a simple slope analysis?

Answer 15

the slope itself can be calculated by sustituting the value of the moderator into the regression equation. The slope itself: b1+b3M

Question 16

Step 5 - Simple Slope analysis (Option 2)

Answer 16

• rerun regression with adjusted intercation term
• intercation term = mean cenetered independent variable * (mean cenetered moderator +/-SD)
• enter adjusted intercation term
• Coefficient of main effect = simple slope