Interaction between two continuous variables

From PsychWiki - A Collaborative Psychology Wiki

(Difference between revisions)
Jump to: navigation, search
Stenstro (Talk | contribs)
Line 13: Line 13:
*#:the interaction = X1*X2,  
*#:the interaction = X1*X2,  
*#:Y = running speed
*#:Y = running speed
-
*#Y<sub>''i''</sub> = ''b''<sub>0</sub> + ''b''<sub>1</sub>X1<sub>''i''</sub> + ''b''<sub>2</sub>X2<sub>''i''</sub> + ''b''<sub>3</sub>(X1<sub>''i''</sub> X2<sub>''i''</sub>) + ''e<sub>i</sub>''
+
*#Here is the formula for: Running speed = intercept + b1energu drink + b2energy bar + b3(bar * drink) + ei
-
+
*#:Y<sub>''i''</sub> = ''b''<sub>0</sub> + ''b''<sub>1</sub>X1<sub>''i''</sub> + ''b''<sub>2</sub>X2<sub>''i''</sub> + ''b''<sub>3</sub>(X1<sub>''i''</sub> X2<sub>''i''</sub>) + ''e<sub>i</sub>''
-
Running speed = intercept + b1energu drink + b2energy bar + b3(bar * drink) + ei
+
*#This formula can be rewritten as
 +
*#:Y<sub>''i''</sub> = (''b''<sub>0</sub> + ''b''<sub>2</sub>X<sub>2''i''</sub>) + (''b''<sub>1</sub>+ ''b''<sub>3</sub>X<sub>2''i''</sub>) X<sub>1''i''</sub> + ''e<sub>i</sub>''
 +
*#:where (''b''<sub>1</sub>+ ''b''<sub>3</sub>X<sub>2''i''</sub>) represents the effect of X<sub>1</sub> on Y at specific levels of X<sub>2</sub>
 +
*#:and ''b<sub>3</sub>'' indicates how much the slope of X<sub>1</sub> changes as X<sub>2</sub> goes up or down one unit.
 +
*#It is then possible to factor out X<sub>2</sub>
 +
<sub>

Revision as of 05:43, 30 October 2006

Statistical programs, like SPSS, do not always have "point-and-click" commands for every possible statistical test. This page is a description of how to test the interaction between two continuous variables. Below, an explanation of interactions is presented, then the three steps to conduct the interaction is described, and examples are given to help in understanding the steps involved.

What is an interaction?


Three Steps

==Plotting the interaction==

Personal tools
Namespaces
Variants
Actions
Navigation
Interaction
Toolbox